Flt3 binding proteins and methods of use

ABSTRACT

Provided herein are FLT3 binding proteins, pharmaceutical compositions comprising such proteins or fragments thereof, as well as nucleic acids, recombinant expression vectors and host cells for making such FLT3 binding proteins. Also disclosed are methods of using the disclosed FLT3 binding proteins in the prevention, and/or treatment of diseases, conditions and disorders.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No. 17/180,435 filed on Feb. 19, 2021, and claims the benefit of U.S. Provisional Application No. 62/980,051 filed on Feb. 21, 2020, all of which are incorporated by reference herein in their entirety.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Feb. 19, 2021, is named 47517-744_201_SL.txt and is 532,727 bytes in size.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

BACKGROUND

FMS-like tyrosine kinase 3 (FLT3) is a type I transmembrane protein that plays an essential role in normal hematopoiesis and is physiologically expressed on normal hematopoietic stem cells (HSCs), as well as lymphoid, myeloid and granulocyte/macrophage progenitor cells in humans, and are believed to play an important role in early hematopoiesis. In mature hematopoietic cells, FLT3 expression has been reported in subsets of dendritic cells and natural killer cells. Due to its important role in regulating survival, proliferation, and differentiation of hematopoietic cells (B and T cells), aberrant FLT3 activity is involved in the development and progression of cancers of the hematopoietic system. For example, internal tandem duplications of FLT3 are the most common mutations associated with acute myelogenous leukemia (AML). FLT3 is also present on malignant blasts in AML, providing a target for antibody and cellular immunotherapy1. As such, there is a need for therapies, e.g., antibodies, that can specifically target and destroy cells that overexpress FLT3. Further, there is a need for a greater choice of treatment options which allows physicians to select the therapeutic with the best side effect profile for an individual patient. The present disclosure provides novel polypeptides and protein therapeutics useful in methods of treatment, particularly for treatment of conditions associated with abnormal expression of FLT3.

SUMMARY

One embodiment provides an FLT3 binding domain comprising at least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein

-   -   the CDR1 comprises a sequence selected from the group consisting         of SEQ ID Nos. 77-108, or a sequence comprising one or more         amino acid substitutions in a sequence selected from the group         consisting of SEQ ID Nos. 77-108;     -   the CDR2 comprises a sequence selected from the group consisting         of SEQ ID Nos. 109-154, and 393-394, or a sequence comprising         one or more amino acid substitutions in a sequence selected from         the group consisting of SEQ ID Nos. 109-154, and 393-394;     -   the CDR3 comprises a sequence selected from the group consisting         of SEQ ID Nos. 155-195, or a sequence comprising one or more         amino acid substitutions in a sequence selected from the group         consisting of SEQ ID Nos. 155-195.

In some embodiments, the FLT3 binding domain of claim 1, comprising at least one of the following set of sequences (the CDR1, the CDR2, and the CDR3):

-   -   SEQ ID Nos. 77, 109, and 155;     -   SEQ ID Nos. 78, 109, and 155;     -   SEQ ID Nos. 79, 110, and 156;     -   SEQ ID Nos. 80, 111, and 155;     -   SEQ ID Nos. 81, 112, and 155;     -   SEQ ID Nos. 77, 113, and 157;     -   SEQ ID Nos. 82, 110, and 156;     -   SEQ ID Nos. 77, 114, and 158;     -   SEQ ID Nos. 80, 111, and 155;     -   SEQ ID Nos. 83, 115, and 155;     -   SEQ ID Nos. 84, 111, and 155;     -   SEQ ID Nos. 79, 116, and 156;     -   SEQ ID Nos. 85, 111, and 155;     -   SEQ ID Nos. 86, 110, and 156;     -   SEQ ID Nos. 87, 110, and 156;     -   SEQ ID Nos. 88, 117, and 159;     -   SEQ ID Nos. 88, 118, and 160;     -   SEQ ID Nos. 88, 119, and 161;     -   SEQ ID Nos. 88, 120, and 162;     -   SEQ ID Nos. 88, 121, and 163;     -   SEQ ID Nos. 88, 122, and 164;     -   SEQ ID Nos. 88, 121, and 165;     -   SEQ ID Nos. 88, 121, and 166;     -   SEQ ID Nos. 88, 122, and 167;     -   SEQ ID Nos. 88, 122, and 168;     -   SEQ ID Nos. 88, 121, and 169;     -   SEQ ID Nos. 88, 118, and 165;     -   SEQ ID Nos. 88, 123, and 170;     -   SEQ ID Nos. 88, 124, and 171;     -   SEQ ID Nos. 88, 117, and 172;     -   SEQ ID Nos. 89, 125, and 173;     -   SEQ ID Nos. 90, 126, and 174;     -   SEQ ID Nos. 90, 127, and 175;     -   SEQ ID Nos. 90, 125, and 176;     -   SEQ ID Nos. 90, 128, and 175;     -   SEQ ID Nos. 90, 128, and 177;     -   SEQ ID Nos. 91, 129, and 178;     -   SEQ ID Nos. 91, 130, and 178;     -   SEQ ID Nos. 92, 131, and 178;     -   SEQ ID Nos. 93, 132, and 178;     -   SEQ ID Nos. 94, 133, and 179;     -   SEQ ID Nos. 91, 134, and 178;     -   SEQ ID Nos. 95, 135, and 180;     -   SEQ ID Nos. 96, 136, and 181;     -   SEQ ID Nos. 97, 137, and 182;     -   SEQ ID Nos. 97, 138, and 183;     -   SEQ ID Nos. 98, 139, and 184;     -   SEQ ID Nos. 99, 139, and 185;     -   SEQ ID Nos. 100, 140, and 186;     -   SEQ ID Nos. 101, 141, and 187;     -   SEQ ID Nos. 102, 142, and 188;     -   SEQ ID Nos. 103, 143, and 189;     -   SEQ ID Nos. 104, 144, and 190;     -   SEQ ID Nos. 105, 145, and 191;     -   SEQ ID Nos. 106, 146, and 192;     -   SEQ ID Nos. 107, 147, and 193;     -   SEQ ID Nos. 108, 148, and 194;     -   SEQ ID Nos. 91, 149, and 195;     -   SEQ ID Nos. 91, 150, and 195;     -   SEQ ID Nos. 100, 151, and 186;     -   SEQ ID Nos. 92, 152, and 195;     -   SEQ ID Nos. 93, 153, and 195;     -   SEQ ID Nos. 91, 154, and 195;     -   SEQ ID Nos. 89, 393, and 173; and     -   SEQ ID Nos. 89, 394, and 173.

In some embodiments, the FLT3 binding domain comprises at least one of the following set of sequences (the CDR1, the CDR2, and the CDR3):

-   -   SEQ ID Nos. 89, 393, and 173;     -   SEQ ID Nos. 89, 394, and 173;     -   SEQ ID Nos. 100, 151, and 186; and     -   SEQ ID Nos. 91, 149, and 195.

In some embodiments, wherein the binding domain further comprises a framework region 1, a framework region 2, a framework region 3, and a framework region 4, wherein the framework region 1 comprises a sequence selected from the group consisting of SEQ ID Nos. 273-301, the framework region 2 comprises a sequence selected from the group consisting of SEQ ID Nos. 302-322, 395, and 406-407, the framework region 3 comprises a sequence selected from the group consisting of SEQ ID Nos. 323-365, and 396, and the framework region 4 comprises a sequence selected from the group consisting of SEQ ID Nos. 366-371. In some embodiments, the FLT3 binding domain comprises sequence that is at least about 60% identical to a sequence selected from the group consisting of SEQ ID Nos. 1-76, and 389-390. In some embodiments, the FLT3 binding domain comprises a sequence that is at least about 70% identical to a sequence selected from the group consisting of SEQ ID Nos. 71-76, and 389-390.

In some embodiments, the FLT3 binding domain comprises the FLT3 binding domain is an antibody or an antigen binding fragment thereof. In some embodiments, the antibody or an antigen binding fragment thereof comprises at least one of: a monoclonal antibody (mAb), a bispecific antibody, a trispecific antibody, a monovalent antibody, a multivalent antibody, an hcIgG, an Fv, an Fd, an Fab, an F(ab′)2, an F(ab′), an Fab2, an Fab3, an scFab, an scFv, an scFvFc, an scFv-zipper, a di-scFv, a tandem scFv, an sdFv, an sdAb, a VH domain, a VL domain, a VHH domain, a half-antibody, a diabody, a single chain diabody, a tandem diabody, a tandem di-scFv, or a tandem tri-scFv. In some embodiments, the FLT3 binding domain is the sdAb. In some embodiments, the FLT3 binding domain is part of an antibody or an antigen binding fragment thereof. In some embodiments, the antibody or an antigen binding fragment thereof comprises at least one of: a monoclonal antibody (mAb), a bispecific antibody, a multispecific antibody, a monovalent antibody, a multivalent antibody, an hcIgG, an Fv, an Fd, an Fab, an F(ab′)2, an F(ab′), an Fab2, an Fab3, an scFab, an scFv, an scFvFc, an scFv-zipper, a di-scFv, a tandem scFv, a half-antibody, a diabody, a single chain diabody, a tandem diabody, a tandem di-scFv, or a tandem tri-scFv. In some embodiments, the FLT3 binding domain is part of the antibody or an antigen binding fragment thereof and wherein the antibody or an antigen binding fragment thereof comprises the bispecific antibody.

In some embodiments, the FLT3 binding domain comprises the bispecific antibody comprises (i) the FLT3 binding domain (anti-FLT3) and (ii) a CD3 binding domain. In some embodiments, the FLT3 binding domain comprises the CD3 comprises a human CD3. In some embodiments, the anti-FLT3 domain is an sdAb. In some embodiments, the anti-CD3 domain is an scFv. In some embodiments, the FLT3 binding domain is part of the antibody or an antigen binding fragment thereof and wherein the antibody or an antigen binding fragment thereof comprises the multispecific antibody. In some embodiments, the multispecific antibody comprises (i) the FLT3 binding domain (anti-FLT3); (ii) a CD3 binding domain (anti-CD3); and (iii) an albumin binding domain (anti-ALB). In some embodiments, the CD3 comprises a human CD3. In some embodiments, the albumin comprises a serum albumin. In some embodiments, the serum albumin is a human serum albumin.

In some embodiments, the FLT3 binding domain (anti-FLT3), the CD3 binding domain (anti-CD3), and the albumin binding domain (anti-ALB) are in an at least one of the following formats, from N-terminus to C-terminus:

anti-ALB: anti-FLT3: anti-CD3;

anti-CD3: anti-FLT3: anti-ALB;

anti-FLT3: anti-CD3: anti-ALB;

anti-ALB: anti-CD3: anti-FLT3;

anti-FLT3: anti-ALB: anti-CD3; and

anti-CD3: anti-ALB: anti-FLT3.

In some embodiments, the anti-FLT3 domain is an sdAb. In some embodiments, the anti-CD3 domain is an scFv. In some embodiments, the anti-ALB domain is an sdAb. In some embodiments, the anti-CD3 domain comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 373. In some embodiments, the anti-ALB domain comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 372. In some embodiments, the FLT3 binding domain binds to human FLT3 and cynomolgus FLT3.

One embodiment provides an FLT3 binding domain that has an half-maximal effective concentration (EC₅₀) of at least about 0.5 pM to about 6000 pM in a T-cell dependent cellular cytotoxicity assay, wherein the assay measures the EC₅₀ of the FLT3 binding domain in T cells mediated killing of FLT-3 expressing cells. In some embodiments, the FLT-3 expressing cells are leukemia cells. In some embodiments, the leukemia cells are from a cell line, wherein the cell line is MV-4-11, EOL1, THP1, MOLM3, or HL60. In some embodiments, the FLT3 binding domain comprises least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein

-   -   the CDR1 comprises a sequence selected from the group consisting         of SEQ ID Nos. 89, 91, 92, 93, and 100, or a sequence comprising         one or more amino acid substitutions in a sequence selected from         the group consisting of SEQ ID Nos. 89, 91, 92, 93, and 100;     -   the CDR2 comprises a sequence selected from the group consisting         of SEQ ID Nos. 149, 150, 151, 152, 153, 154, 393, and 394, or a         sequence comprising one or more amino acid substitutions in a         sequence selected from the group consisting of SEQ ID Nos. 149,         150, 151, 152, 153, 154, 393, and 394;     -   the CDR3 comprises a sequence selected from the group consisting         of SEQ ID Nos. 173, 186, and 195, or a sequence comprising one         or more amino acid substitutions in a sequence selected from the         group consisting of SEQ ID Nos. 173, 186, and 195.

In some embodiments, the FLT3 binding domain comprises at least one of the following set of sequences (the CDR1, the CDR2, and the CDR3):

-   -   SEQ ID Nos. 91, 149, and 195;     -   SEQ ID Nos. 91, 150, and 195;     -   SEQ ID Nos. 100, 151, and 186;     -   SEQ ID Nos. 92, 152, and 195;     -   SEQ ID Nos. 93, 153, and 195;     -   SEQ ID Nos. 91, 154, and 195;     -   SEQ ID Nos. 89, 393, and 173; and     -   SEQ ID Nos. 89, 394, and 173.

In some embodiments, the FLT3 binding domain comprises a sequence that is at least about 70% identical to a sequence selected from the group consisting of SEQ ID Nos. 71-76, and 389-390.

In some embodiments, the FLT3 binding domain is part of a multispecific antibody. In some embodiments, the multispecific antibody comprises (i) the FLT3 binding domain (anti-FLT3); (ii) a CD3 binding domain (anti-CD3); and (iii) an albumin binding domain (anti-ALB). In some embodiments, the CD3 comprises a human CD3. In some embodiments, the albumin comprises a serum albumin. In some embodiments, the serum albumin is a human serum albumin. In some embodiments, the FLT3 binding domain (anti-FLT3), the CD3 binding domain (anti-CD3), and the albumin binding domain (anti-ALB) are in an at least one of the following formats, from N-terminus to C-terminus:

anti-ALB: anti-FLT3: anti-CD3;

anti-CD3: anti-FLT3: anti-ALB;

anti-FLT3: anti-CD3: anti-ALB;

anti-ALB: anti-CD3: anti-FLT3;

anti-FLT3: anti-ALB: anti-CD3; and

anti-CD3: anti-ALB: anti-FLT3.

In some embodiments, the anti-FLT3 domain is an sdAb. In some embodiments, anti-CD3 domain is an scFv. In some embodiments, the anti-ALB domain is an sdAb. In some embodiments, the anti-CD3 domain comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 373. In some embodiments, the anti-ALB domain comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 372. In some embodiments, the FLT3 binding domain binds to a human FLT3, a cynomolgus FLT3, or both.

One embodiment provides an FLT3 binding domain that binds to a human FLT3 and to a cynomolgus FLT3 with identical affinities or affinities that differ by up to about 58-fold. One embodiment provides an FLT3 targeting trispecific protein comprising

(A) a first domain that binds a human CD3;

(B) a second domain that binds a human serum albumin protein; and

(C) a third domain that binds a human FLT3 or a cynomolgus FLT3,

wherein the domains are linked according to any one of the following orientations, from N-terminus to C-terminus: H₂N-(A)-(C)-(B)-COOH, H₂N-(B)-(A)-(C)-COOH, H₂N-(C)-(B)-(A)-COOH, H₂N-(C)-(A)-(B)-COOH, H₂N-(A)-(B)-(C)-COOH, or H₂N-(B)-(C)-(A)-COOH, or via linkers L1 and L2, from N-terminus to C-terminus: H₂N-(A)-L1-(C)-L2-(B)-COOH, H₂N-(B)-L1-(A)-L2-(C)-COOH, H₂N-(C)-L1-(B)-L2-(A)-COOH, H₂N-(C)-L1-(A)-L2-(B)-COOH, H₂N-(A)-L1-(B)-L2-(C)-COOH, or H₂N-(B)-L1-(C)-L2-(A)-COOH.

In some embodiments, the first domain is an scFv that comprises a heavy chain comprising HC CDR1, HC CDR2, HC CDR3, and a light chain comprising LC CDR1, LC CDR2, or LC CDR3, wherein the HC CDR1 comprises the amino acid sequence of SEQ ID NO: 397 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 397; the HC CDR2 comprises the amino acid sequence of SEQ ID NO: 398 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 398; the HC CDR3 comprises the amino acid sequence of SEQ ID NO: 399 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 399; the LC CDR1 comprises the amino acid sequence of SEQ ID NO: 400 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 400; the LC CDR2 comprises the amino acid sequence of SEQ ID NO: 401 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 401; and the LC CDR3 comprises the amino acid sequence of SEQ ID NO: 402 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 402. In some embodiments, the first domain is an scFv that comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 373. In some embodiments, the second domain is an sdAb that comprises a CDR1, a CDR2, and a CDR3, wherein the CDR1 comprises the amino acid sequence of SEQ ID NO: 403 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 403; the CDR2 comprises the amino acid sequence of SEQ ID NO: 404 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 404; and the CDR3 comprises the amino acid sequence of SEQ ID NO: 405 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 405.

In some embodiments, the second domain is an sdAb that comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 372. In some embodiments, the third domain is an sdAb comprising at least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein

-   -   the CDR1 comprises a sequence selected from the group consisting         of SEQ ID Nos. 77-108, or a sequence comprising one or more         amino acid substitutions in a sequence selected from the group         consisting of SEQ ID Nos. 77-108;     -   the CDR2 comprises a sequence selected from the group consisting         of SEQ ID Nos. 109-154, and 393-394, or a sequence comprising         one or more amino acid substitutions in a sequence selected from         the group consisting of SEQ ID Nos. 109-154, and 393-394;     -   the CDR3 comprises a sequence selected from the group consisting         of SEQ ID Nos. 155-195, or a sequence comprising one or more         amino acid substitutions in a sequence selected from the group         consisting of SEQ ID Nos. 155-195.

In some embodiments, the third domain comprises at least one of the following set of sequences (the CDR1, the CDR2, and the CDR3):

-   -   SEQ ID Nos. 77, 109, and 155;     -   SEQ ID Nos. 78, 109, and 155;     -   SEQ ID Nos. 79, 110, and 156;     -   SEQ ID Nos. 80, 111, and 155;     -   SEQ ID Nos. 81, 112, and 155;     -   SEQ ID Nos. 77, 113, and 157;     -   SEQ ID Nos. 82, 110, and 156;     -   SEQ ID Nos. 77, 114, and 158;     -   SEQ ID Nos. 80, 111, and 155;     -   SEQ ID Nos. 83, 115, and 155;     -   SEQ ID Nos. 84, 111, and 155;     -   SEQ ID Nos. 79, 116, and 156;     -   SEQ ID Nos. 85, 111, and 155;     -   SEQ ID Nos. 86, 110, and 156;     -   SEQ ID Nos. 87, 110, and 156;     -   SEQ ID Nos. 88, 117, and 159;     -   SEQ ID Nos. 88, 118, and 160;     -   SEQ ID Nos. 88, 119, and 161;     -   SEQ ID Nos. 88, 120, and 162;     -   SEQ ID Nos. 88, 121, and 163;     -   SEQ ID Nos. 88, 122, and 164;     -   SEQ ID Nos. 88, 121, and 165;     -   SEQ ID Nos. 88, 121, and 166;     -   SEQ ID Nos. 88, 122, and 167;     -   SEQ ID Nos. 88, 122, and 168;     -   SEQ ID Nos. 88, 121, and 169;     -   SEQ ID Nos. 88, 118, and 165;     -   SEQ ID Nos. 88, 123, and 170;     -   SEQ ID Nos. 88, 124, and 171;     -   SEQ ID Nos. 88, 117, and 172;     -   SEQ ID Nos. 89, 125, and 173;     -   SEQ ID Nos. 90, 126, and 174;     -   SEQ ID Nos. 90, 127, and 175;     -   SEQ ID Nos. 90, 125, and 176;     -   SEQ ID Nos. 90, 128, and 175;     -   SEQ ID Nos. 90, 128, and 177;     -   SEQ ID Nos. 91, 129, and 178;     -   SEQ ID Nos. 91, 130, and 178;     -   SEQ ID Nos. 92, 131, and 178;     -   SEQ ID Nos. 93, 132, and 178;     -   SEQ ID Nos. 94, 133, and 179;     -   SEQ ID Nos. 91, 134, and 178;     -   SEQ ID Nos. 95, 135, and 180;     -   SEQ ID Nos. 96, 136, and 181;     -   SEQ ID Nos. 97, 137, and 182;     -   SEQ ID Nos. 97, 138, and 183;     -   SEQ ID Nos. 98, 139, and 184;     -   SEQ ID Nos. 99, 139, and 185;     -   SEQ ID Nos. 100, 140, and 186;     -   SEQ ID Nos. 101, 141, and 187;     -   SEQ ID Nos. 102, 142, and 188;     -   SEQ ID Nos. 103, 143, and 189;     -   SEQ ID Nos. 104, 144, and 190;     -   SEQ ID Nos. 105, 145, and 191;     -   SEQ ID Nos. 106, 146, and 192;     -   SEQ ID Nos. 107, 147, and 193;     -   SEQ ID Nos. 108, 148, and 194;     -   SEQ ID Nos. 91, 149, and 195;     -   SEQ ID Nos. 91, 150, and 195;     -   SEQ ID Nos. 100, 151, and 186;     -   SEQ ID Nos. 92, 152, and 195;     -   SEQ ID Nos. 93, 153, and 195;     -   SEQ ID Nos. 91, 154, and 195;     -   SEQ ID Nos. 89, 393, and 173; and     -   SEQ ID Nos. 89, 394, and 173.

In some embodiments, the FLT3 targeting trispecific protein comprises a sequence selected from the group consisting of SEQ ID Nos. 196-272, and 391-392, or a sequence that is at least about 80% identical to a sequence selected from the group consisting of SEQ ID NOs: 196-272, and 391-392.

One embodiment provides an FLT3 targeting conditionally active binding protein comprising a binding moiety which comprises a non-CDR loop, a cleavable linker, an FLT3 binding domain, and a CD3 binding domain, wherein the non-CDR loop is capable of binding to the FLT3 binding domain, and wherein the binding moiety is capable of masking the binding of the FLT3 binding domain to its target. In some embodiments, the CD3 binding domain is an scFv that comprises a heavy chain comprising HC CDR1, HC CDR2, HC CDR3, and a light chain comprising LC CDR1, LC CDR2, or LC CDR3, wherein the HC CDR1 comprises the amino acid sequence of SEQ ID NO: 397 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 397; the HC CDR2 comprises the amino acid sequence of SEQ ID NO: 398 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 398; the HC CDR3 comprises the amino acid sequence of SEQ ID NO: 399 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 399; the LC CDR1 comprises the amino acid sequence of SEQ ID NO: 400 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 400; the LC CDR2 comprises the amino acid sequence of SEQ ID NO: 401 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 401; and the LC CDR3 comprises the amino acid sequence of SEQ ID NO: 402 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 402.

In some embodiments, the CD3 binding domain is an scFv that comprises an amino acid sequence that is at least about 90% identical to the sequence set forth in SEQ ID No. 373. In some embodiments, the FLT3 binding domain is an sdAb comprising at least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein

-   -   the CDR1 comprises a sequence selected from the group consisting         of SEQ ID Nos. 77-108, or a sequence comprising one or more         amino acid substitutions in a sequence selected from the group         consisting of SEQ ID Nos. 77-108;     -   the CDR2 comprises a sequence selected from the group consisting         of SEQ ID Nos. 109-154, and 393-394, or a sequence comprising         one or more amino acid substitutions in a sequence selected from         the group consisting of SEQ ID Nos. 109-154, and 393-394;     -   the CDR3 comprises a sequence selected from the group consisting         of SEQ ID Nos. 155-195, or a sequence comprising one or more         amino acid substitutions in a sequence selected from the group         consisting of SEQ ID Nos. 155-195.

In some embodiments, the FLT3 binding domain comprises at least one of the following set of sequences (the CDR1, the CDR2, and the CDR3):

-   -   SEQ ID Nos. 77, 109, and 155;     -   SEQ ID Nos. 78, 109, and 155;     -   SEQ ID Nos. 79, 110, and 156;     -   SEQ ID Nos. 80, 111, and 155;     -   SEQ ID Nos. 81, 112, and 155;     -   SEQ ID Nos. 77, 113, and 157;     -   SEQ ID Nos. 82, 110, and 156;     -   SEQ ID Nos. 77, 114, and 158;     -   SEQ ID Nos. 80, 111, and 155;     -   SEQ ID Nos. 83, 115, and 155;     -   SEQ ID Nos. 84, 111, and 155;     -   SEQ ID Nos. 79, 116, and 156;     -   SEQ ID Nos. 85, 111, and 155;     -   SEQ ID Nos. 86, 110, and 156;     -   SEQ ID Nos. 87, 110, and 156;     -   SEQ ID Nos. 88, 117, and 159;     -   SEQ ID Nos. 88, 118, and 160;     -   SEQ ID Nos. 88, 119, and 161;     -   SEQ ID Nos. 88, 120, and 162;     -   SEQ ID Nos. 88, 121, and 163;     -   SEQ ID Nos. 88, 122, and 164;     -   SEQ ID Nos. 88, 121, and 165;     -   SEQ ID Nos. 88, 121, and 166;     -   SEQ ID Nos. 88, 122, and 167;     -   SEQ ID Nos. 88, 122, and 168;     -   SEQ ID Nos. 88, 121, and 169;     -   SEQ ID Nos. 88, 118, and 165;     -   SEQ ID Nos. 88, 123, and 170;     -   SEQ ID Nos. 88, 124, and 171;     -   SEQ ID Nos. 88, 117, and 172;     -   SEQ ID Nos. 89, 125, and 173;     -   SEQ ID Nos. 90, 126, and 174;     -   SEQ ID Nos. 90, 127, and 175;     -   SEQ ID Nos. 90, 125, and 176;     -   SEQ ID Nos. 90, 128, and 175;     -   SEQ ID Nos. 90, 128, and 177;     -   SEQ ID Nos. 91, 129, and 178;     -   SEQ ID Nos. 91, 130, and 178;     -   SEQ ID Nos. 92, 131, and 178;     -   SEQ ID Nos. 93, 132, and 178;     -   SEQ ID Nos. 94, 133, and 179;     -   SEQ ID Nos. 91, 134, and 178;     -   SEQ ID Nos. 95, 135, and 180;     -   SEQ ID Nos. 96, 136, and 181;     -   SEQ ID Nos. 97, 137, and 182;     -   SEQ ID Nos. 97, 138, and 183;     -   SEQ ID Nos. 98, 139, and 184;     -   SEQ ID Nos. 99, 139, and 185;     -   SEQ ID Nos. 100, 140, and 186;     -   SEQ ID Nos. 101, 141, and 187;     -   SEQ ID Nos. 102, 142, and 188;     -   SEQ ID Nos. 103, 143, and 189;     -   SEQ ID Nos. 104, 144, and 190;     -   SEQ ID Nos. 105, 145, and 191;     -   SEQ ID Nos. 106, 146, and 192;     -   SEQ ID Nos. 107, 147, and 193;     -   SEQ ID Nos. 108, 148, and 194;     -   SEQ ID Nos. 91, 149, and 195;     -   SEQ ID Nos. 91, 150, and 195;     -   SEQ ID Nos. 100, 151, and 186;     -   SEQ ID Nos. 92, 152, and 195;     -   SEQ ID Nos. 93, 153, and 195;     -   SEQ ID Nos. 91, 154, and 195;     -   SEQ ID Nos. 89, 393, and 173; and     -   SEQ ID Nos. 89, 394, and 173.

One embodiment provides a pharmaceutical composition comprising an FLT3 binding domain according to this disclosure, and a pharmaceutically acceptable carrier. One embodiment provides a pharmaceutical composition comprising an FLT3 targeting trispecific protein according to this disclosure, and a pharmaceutically acceptable carrier. One embodiment provides a pharmaceutical composition comprising an FLT3 targeting conditionally active binding protein according to this disclosure, and a pharmaceutically acceptable carrier. One embodiment provides a process for the production of an FLT3 binding domain according to any this disclosure, said process comprising culturing a host transformed or transfected with a vector comprising a nucleic acid sequence encoding the FLT3 binding domain according to this disclosure under conditions allowing the expression of the FLT3 binding domain and recovering and purifying the produced protein from the culture. One embodiment provides a process for the production of an FLT3 targeting trispecific protein according to this disclosure, said process comprising culturing a host transformed or transfected with a vector comprising a nucleic acid sequence encoding the FLT3 targeting trispecific protein according to this disclosure under conditions allowing the expression of the FLT3 targeting trispecific protein and recovering and purifying the produced protein from the culture.

One embodiment provides a process for the production of an FLT3 targeting conditionally active binding protein according to this disclosure, said process comprising culturing a host transformed or transfected with a vector comprising a nucleic acid sequence encoding the FLT3 targeting conditionally active binding protein according to this disclosure under conditions allowing the expression of the FLT3 targeting conditionally active binding protein and recovering and purifying the produced protein from the culture. One embodiment provides a method for the treatment or amelioration of a proliferative disease, or a tumorous disease, comprising the administration of an FLT3 binding domain according to this disclosure, or a pharmaceutical composition according to this disclosure, to a subject in need thereof. One embodiment provides a method for the treatment or amelioration of a proliferative disease, or a tumorous disease, comprising the administration of an FLT3 targeting trispecific protein according to this disclosure, or a pharmaceutical composition according to this disclosure, to a subject in need thereof. One embodiment provides a method for the treatment or amelioration of a proliferative disease, or a tumorous disease, comprising the administration of an FLT3 targeting conditionally active binding protein according to this disclosure, or a pharmaceutical composition according to claim this disclosure, to a subject in need thereof.

In some embodiments, the subject is human. In some embodiments, the method further comprises administration of an agent in combination with an FLT3 binding domain according to this disclosure, an FLT3 targeting trispecific protein according to this disclosure, an FLT3 targeting conditionally active binding protein according to this disclosure, or a pharmaceutical composition according to this disclosure. In some embodiments, the tumorous disease comprises a hematologic malignancy. In some embodiments, the hematologic malignancy comprises an acute myeloid leukemia (AML), myelodysplastic syndrome, or chronic myelomonocytic leukemia. In some embodiments, the tumorous disease is selected from the group consisting of: acute leukemia (ALL), acute myelogenous leukemia (AML), myeloid leukemia, chronic lymphocytic leukemia (CLL), and chronic myelogenous leukemia (CIVIL), chronic myelomonocytic leukemia, undifferentiated AML (MO), myeloblastic leukemia (M1), myeloblastic leukemia (M2; with cell maturation), promyelocytic leukemia (M3 or M3 variant [M3V]), myelomonocytic leukemia (M4 or M4 variant with eosinophilia [M4E]), monocytic leukemia (M5), erythroleukemia (M6), megakaryoblastic leukemia (M7), isolated granulocytic sarcoma, and chloroma; lymphomas, such as Hodgkin's lymphoma (HL), non-Hodgkin's lymphoma (NEIL), B-cell lymphomas, T-cell lymphomas, lymphoplasmacytoid lymphoma, monocytoid B-cell lymphoma, mucosa-associated lymphoid tissue (MALT) lymphoma, anaplastic (e.g., Ki 1+) large-cell lymphoma, adult T-cell lymphoma/leukemia, mantle cell lymphoma, angio immunoblastic T-cell lymphoma, angiocentric lymphoma, intestinal T-cell lymphoma, primary mediastinal B-cell lymphoma, precursor T-lymphoblastic lymphoma, T-lymphoblastic; and lymphoma/leukemia (T-Lbly/T-ALL), peripheral T-cell lymphoma, lymphoblastic lymphoma, post-transplantation lymphoproliferative disorder, true histiocytic lymphoma, primary central nervous system lymphoma, primary effusion lymphoma, lymphoblastic lymphoma (LBL), hematopoietic tumors of lymphoid lineage, acute lymphoblastic leukemia, diffuse large B-cell lymphoma, Burkitt's lymphoma, marginal zone lymphoma, nodal marginal zone B cell lymphoma, splenic marginal zone lymphoma, follicular lymphoma, diffuse histiocytic lymphoma (DHL), mucosa-associated lymphatic tissue lymphoma, small cell lymphocytic lymphoma, immunoblastic large cell lymphoma, precursor B-lymphoblastic lymphoma, cutaneous T-cell lymphoma (CTLC) (also called mycosis fungoides or Sezary syndrome), intravascular large B-cell lymphoma, lymphomatoid granulomatosis, T cell/histiocyte-rich large B-cell lymphoma, primary cutaneous diffuse large B-cell lymphoma (leg type), EBV positive diffuse large B-cell lymphoma of the elderly, diffuse large B-cell lymphoma associated with inflammation, intravascular large B-cell lymphoma, ALK-positive large B-cell lymphoma, plasmablastic lymphoma, large B-cell lymphoma arising in HHV8-associated multicentric Castleman disease, B-cell lymphoma unclassified with features intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma, B-cell lymphoma unclassified with features intermediate between diffuse large B-cell lymphoma and classical Hodgkin lymphomalymphoplasmactyic lymphoma, and lymphoplasmacytoid lymphoma (LPL) with Waldenstrom's macroglobulinemia; myelomas, such as IgG myeloma, light chain myeloma, nonsecretory myeloma, smoldering myeloma (also called indolent myeloma), solitary plasmocytoma, and multiple myelomas, chronic lymphocytic leukemia (CLL), hairy cell lymphoma; hematopoietic tumors of myeloid lineage, tumors of mesenchymal origin, including fibrosarcoma and rhabdomyoscarcoma; seminoma, teratocarcinoma, tumors of the central and peripheral nervous, including astrocytoma, schwannomas; tumors of mesenchymal origin, including fibrosarcoma, rhabdomyoscaroma, and osteosarcoma; and other tumors, including melanoma, xeroderma pigmentosum, keratoacanthoma, seminoma, thyroid follicular cancer and teratocarcinoma, hematopoietic tumors of lymphoid lineage, for example T-cell and B-cell tumors, including but not limited to T-cell disorders such as T-prolymphocytic leukemia (T-PLL), including of the small cell and cerebriform cell type; large granular lymphocyte leukemia (LGL) preferably of the T-cell type; a/d T-NHL hepatosplenic lymphoma; peripheral/post-thymic T cell lymphoma (pleomorphic and immunoblastic subtypes); angiocentric (nasal) T-cell lymphoma; cancer of the head or neck, renal cancer, rectal cancer, cancer of the thyroid gland; acute myeloid lymphoma, as well as any combinations thereof.

One embodiment provides an FLT3 binding domain comprising at least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein

-   -   the CDR1 comprises a sequence selected from the group consisting         of SEQ ID Nos. 89, 91, and 100, or a sequence comprising one or         more amino acid substitutions in a sequence selected from the         group consisting of SEQ ID Nos. 89, 91, and 100;     -   the CDR2 comprises a sequence selected from the group consisting         of SEQ ID Nos. 149, 151, 393, and 394, or a sequence comprising         one or more amino acid substitutions in a sequence selected from         the group consisting of SEQ ID Nos. 149, 151, 393, and 394;     -   the CDR3 comprises a sequence selected from the group consisting         of SEQ ID Nos. 173, 186, and 195, or a sequence comprising one         or more amino acid substitutions in a sequence selected from the         group consisting of SEQ ID Nos. 173, 186, and 195.

In some embodiments, the FLT3 binding domain comprises at least one of the following set of sequences (the CDR1, the CDR2, and the CDR3):

-   -   SEQ ID Nos. 89, 393, and 173;     -   SEQ ID Nos. 89, 394, and 173;     -   SEQ ID Nos. 100, 151, and 186; and     -   SEQ ID Nos. 91, 149, and 195.

In some embodiments, the FLT3 binding domain comprises an amino acid sequence that is at least 80% identical to a sequence selected from the group consisting of SEQ ID Nos. 71, 73, 389, and 390. In some embodiments, the FLT3 binding domain comprises an amino acid sequence selected from the group consisting of SEQ ID Nos. 71, 73, 389, and 390. In some embodiments, the FLT3 binding domain is a single domain antibody (sdAb). In some embodiments, the FLT3 binding domain is part of an antibody or an antigen binding fragment thereof. In some embodiments, the FLT3 binding domain comprises is part of the antibody or an antigen binding fragment thereof and wherein the antibody or an antigen binding fragment thereof comprises a bispecific antibody. In some embodiments, the bispecific antibody comprises (i) the FLT3 binding domain (anti-FLT3) and (ii) a CD3 binding domain (anti-CD3). In some embodiments, the anti-CD3 domain is a single chain variable fragment (scFv). In some embodiments, the CD3 comprises a human CD3.

In some embodiments, the FLT3 binding domain is part of the antibody or an antigen binding fragment thereof and wherein the antibody or an antigen binding fragment thereof comprises a multispecific antibody. In some embodiments, the multispecific antibody comprises (i) the FLT3 binding domain (anti-FLT3); (ii) a CD3 binding domain (anti-CD3); and (iii) an albumin binding domain (anti-ALB). In some embodiments, the anti-CD3 domain is an scFv. In some embodiments, the anti-CD3 domain comprises an amino acid sequence that is at least 90% identical to the sequence of SEQ ID No. 373. In some embodiments, the CD3 comprises a human CD3. In some embodiments, the anti-ALB domain is an sdAb. In some embodiments, the anti-ALB domain comprises an amino acid sequence that is at least 90% identical to the sequence of SEQ ID No. 372.

In some embodiments, the albumin comprises a human serum albumin. In some embodiments, the FLT3 binding domain (anti-FLT3), the CD3 binding domain (anti-CD3), and the albumin binding domain (anti-ALB) are in an at least one of the following formats, from N-terminus to C-terminus:

anti-ALB: anti-FLT3: anti-CD3;

anti-CD3: anti-FLT3: anti-ALB;

anti-FLT3: anti-CD3: anti-ALB;

anti-ALB: anti-CD3: anti-FLT3;

anti-FLT3: anti-ALB: anti-CD3; and

anti-CD3: anti-ALB: anti-FLT3.

In some embodiments, the FLT3 binding domain is part of the multispecific antibody, wherein the multispecific antibody comprises a sequence that is at least 80% identical to a sequence selected from the group consisting of SEQ ID Nos. 267, 269, 391, and 392. In some embodiments, the FLT3 binding domain binds to human FLT3.

One embodiment provides an FLT3 targeting trispecific protein comprising

-   -   (A) a first domain that binds a human CD3;     -   (B) a second domain that binds a human serum albumin protein;         and     -   (C) a third domain that binds a human FLT3,     -   wherein the CDR1 comprises a sequence selected from the group         consisting of SEQ ID Nos. 89, 91, and 100, or a sequence         comprising one or more amino acid substitutions in a sequence         selected from the group consisting of SEQ ID Nos. 89, 91, and         100; the CDR2 comprises a sequence selected from the group         consisting of SEQ ID Nos. 149, 151, 393, and 394, or a sequence         comprising one or more amino acid substitutions in a sequence         selected from the group consisting of SEQ ID Nos. 149, 151, 393,         and 394; and the CDR3 comprises a sequence selected from the         group consisting of SEQ ID Nos. 173, 186, and 195, or a sequence         comprising one or more amino acid substitutions in a sequence         selected from the group consisting of SEQ ID Nos. 173, 186, and         195.

In some embodiments, the first domain is an scFv that comprises a heavy chain comprising HC CDR1, HC CDR2, HC CDR3, and a light chain comprising LC CDR1, LC CDR2, or LC CDR3, wherein the HC CDR1 comprises the amino acid sequence of SEQ ID NO: 397 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 397; the HC CDR2 comprises the amino acid sequence of SEQ ID NO: 398 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 398; the HC CDR3 comprises the amino acid sequence of SEQ ID NO: 399 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 399; the LC CDR1 comprises the amino acid sequence of SEQ ID NO: 400 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 400; the LC CDR2 comprises the amino acid sequence of SEQ ID NO: 401 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 401; and the LC CDR3 comprises the amino acid sequence of SEQ ID NO: 402 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 402. In some embodiments, the first domain is an scFv that comprises an amino acid sequence that is at least 90% identical to the sequence set forth in SEQ ID No. 373. In some embodiments, the FLT3 targeting trispecific protein of claim 22, wherein the second domain is an sdAb that comprises a CDR1, a CDR2, and a CDR3, wherein the CDR1 comprises the amino acid sequence of SEQ ID NO: 403 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 403; the CDR2 comprises the amino acid sequence of SEQ ID NO: 404 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 404; and the CDR3 comprises the amino acid sequence of SEQ ID NO: 405 or an amino acid sequence comprising one or more substitutions in the sequence of SEQ ID NO: 405. In some embodiments, the FLT3 targeting trispecific protein of claim 25, wherein the second domain is an sdAb that comprises an amino acid sequence that is at least 90% identical to the sequence set forth in SEQ ID No. 372.

One embodiment provides a method of treating a hematologic malignancy, the method comprising administering to a subject in need thereof a FLT3 targeting trispecific protein comprising

-   -   (A) a first domain that binds a human CD3;     -   (B) a second domain that binds a human serum albumin protein;         and     -   (C) a third domain that binds a human FLT3,     -   wherein the CDR1 comprises a sequence selected from the group         consisting of SEQ ID Nos. 89, 91, and 100, or a sequence         comprising one or more amino acid substitutions in a sequence         selected from the group consisting of SEQ ID Nos. 89, 91, and         100; the CDR2 comprises a sequence selected from the group         consisting of SEQ ID Nos. 149, 151, 393, and 394, or a sequence         comprising one or more amino acid substitutions in a sequence         selected from the group consisting of SEQ ID Nos. 149, 151, 393,         and 394; the CDR3 comprises a sequence selected from the group         consisting of SEQ ID Nos. 173, 186, and 195, or a sequence         comprising one or more amino acid substitutions in a sequence         selected from the group consisting of SEQ ID Nos. 173, 186,         and 195. In some embodiments, the third domain comprises an         amino acid sequence that is at least 80% identical to a sequence         selected from the group consisting of SEQ ID Nos. 71, 73, 389,         and 390. In some embodiments, the trispecific protein comprises         an amino acid sequence that is at least 80% identical to a         sequence selected from the group consisting of SEQ ID Nos. 267,         269, 391, and 392. In some embodiments, the hematologic         malignancy comprises an acute myeloid leukemia (AML), a         myelodysplastic syndrome, or a chronic myelomonocytic leukemia.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

FIG. 1 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL21, FLL57, FLL62, FLL1, and FLL103, ran in the presence of 15 mg/ml bovine serum albumin (BSA). The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 2 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL107, FLL112, FLL125, FLL129, and FLL137, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 3 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL14, FLL141, FLL142, FLL143, and FLL146, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 4 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL15, FLL154, FLL158, FLL160, and FLL168, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 5 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL173, FLL177, FLL178, FLL179, and FLL190, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 6 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL26, FLL32, FLL34, FLL38, and FLL39, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 7 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL4, FLL40, FLL43, FLL45, and FLL51, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 8 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL53, FLL55, FLL6, FLL61, and FLL75, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 9 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL76, FLL77, FLL78, FLL82, and FLL822, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 10 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL83, FLL94, and FLL99 and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 11 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL8, FLL41, FLL71, FLL92, FLL134, and FLL153, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 12 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL21, FLL57, FLL62, FLL1, and FLL103, rain in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 13 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL107, FLL112, FLL125, FLL129, and FLL137, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 14 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL14, FLL141, FLL142, FLL143, and FLL146, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 15 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL15, FLL154, FLL158, FLL160, FLL168, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 16 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL173, FLL177, FLL178, FLL179, and FLL190, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 17 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL26, FLL32, FLL34, FLL38, and FLL39, ran the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 18 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL4, FLL40, FLL43, FLL45, and FLL51, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 19 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL53, FLL55, FLL6, FLL61, and FLL75, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 20 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL76, FLL77, FLL78, FLL82, and FLL822, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 21 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL83, FLL94, and FLL99 and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 22 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLL8, FLL41, FLL71, FLL92, FLL134, and FLL153, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 23 illustrates an SDS-PAGE of purified humanized anti-FLT3/anti-albumin/anti-CD3 Multispecific Proteins under non-reducing (first and third panels) and reducing (second and fourth panels) conditions. Lanes 1-8 in order: FLH141, FLH107, FLH34, FLH4, FLH78, FLH19C, FLH92a, FLH92b. The migration of molecular weight standards (in kDa) is indicated by the horizontal lines and the numbers to the left of each gel image.

FIG. 24 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH4, FLH78, FLH19C, FLH141, FLH107, and FLH34 and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells.

FIG. 25 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH4, FLH78, FLH19C, FLH141, FLH107, and FLH34 and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml HSA.

FIG. 26 illustrates the results of a TDCC Assay with EOL1 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH4, FLH78, FLH19C, FLH141, FLH107, and FLH34 and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml BSA.

FIG. 27 illustrates the results of a TDCC Assay with EOL1 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH4, FLH78, FLH19C, FLH141, FLH107, and FLH34 and with a negative control molecule targeting GFP. The assay was run in the presence of 15 mg/ml HSA.

FIG. 28 provides exemplary arrangements of various domains of an FLT3 targeting conditionally active binding protein of this disclosure. The aTarget domain depicted in FIG. 28 Version 1 and Version 2 corresponds to an FLT3 binding domain as described herein.

FIG. 29 illustrates a variable domain of an exemplary immunoglobulin domain, comprising complementarity determining regions (CDR1, CDR2, and CDR3), and non-CDR loops connecting the beta strand (AB, CC′, C″ D, EF, and DE).

FIG. 30 illustrates the results of a TDCC Assay with THP1 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH141, FLH107, FLH34, FLH4, FLH78, FLH19C, FLH92a, FLH92b, without the addition of any type of albumin.

FIG. 31 illustrates the results of a TDCC Assay with THP1 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH141, FLH107, FLH34, FLH4, FLH78, FLH19C, FLH92a, FLH92b, ran in the presence of 15 mg/ml HSA.

FIG. 32 illustrates the results of a TDCC Assay with MOLM13 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH141, FLH107, FLH34, FLH4, FLH78, FLH19C, FLH92a, FLH92b, and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml HSA.

FIG. 33 illustrates the results of a TDCC Assay with HL60 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH141, FLH107, FLH34, FLH4, FLH78, FLH19C, FLH92a, FLH92b, and with a negative control molecule targeting GFP, ran in the presence of 15 mg/ml HSA.

FIG. 34 illustrates the pharmacokinetics of a FLT3 Multispecific Protein Containing Humanized Anti-FLT3 Sequence FLH19C, in cynomolgus monkeys after single i.v. doses of 10 μg/kg, 100 μg/kg, and 1000 μg/kg. Plotted are mean values measured in samples collected from two test subjects per dose group.

FIG. 35 illustrates the amount of soluble FLT3L present in serum samples collected from cynomolgus monkeys after single i.v. doses of 10 μg/kg, 100 μg/kg, and 1000 μg/kg of a FLT3 Multispecific Protein Containing Humanized Anti-FLT3 Sequence FLH19C. Plotted are mean values measured in samples collected from two test subjects per dose group.

FIG. 36 illustrates the amount of FLT3 transcript present in RNA prepared from whole blood collected from cynomolgus monkeys after single i.v. doses of 100 μg/kg and 1000 μg/kg of a FLT3 Multispecific Protein Containing Humanized Anti-FLT3 Sequence FLH19C. Plotted are technical replicates. Data are plotted each individual test subject in each dose group.

FIG. 37 illustrates the amount of FLT3 transcript present in RNA prepared from bone marrow collected from cynomolgus monkeys after single i.v. doses of 100 μg/kg and 1000 μg/kg of a FLT3 Multispecific Protein Containing Humanized Anti-FLT3 Sequence FLH19C. Plotted are technical replicates. Data are plotted for each individual test subject in each dose group.

FIG. 38 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH4, FLH78, FLH19C, FLH141, FLH107, FLH34, FLH92a, and FLH92b, ran in the presence of 15 mg/ml BSA. The y-axis shows the normalized percentage of viability of the cancer cells. The T cells in this assay were obtained from a different donor compared to the assay FIG. 24.

FIG. 39 illustrates the results of a TDCC Assay with MV-4-11 Cells and Anti-CD3/Anti-FLT3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLH4, FLH78, FLH19C, FLH141, FLH107, FLH34, FLH92a, and FLH92b, ran in the presence of 15 mg/ml HSA. The y-axis shows the normalized percentage of viability of the cancer cells. The T cells in this assay were obtained from a different donor compared to the assay in FIG. 25.

DETAILED DESCRIPTION OF THE INVENTION Certain Definitions

The terminology used herein is for the purpose of describing particular cases only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and/or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”

The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, e.g., the limitations of the measurement system. For example, “about” can mean within 1 or more than 1 standard deviation, per the practice in the given value. Where particular values are described in the application and claims, unless otherwise stated the term “about” should be assumed to mean an acceptable error range for the particular value.

The terms “individual,” “patient,” or “subject” are used interchangeably. None of the terms require or are limited to situation characterized by the supervision (e.g. constant or intermittent) of a health care worker (e.g. a doctor, a registered nurse, a nurse practitioner, a physician's assistant, an orderly, or a hospice worker).

An “antibody” typically refers to a Y-shaped tetrameric protein comprising two heavy (H) and two light (L) polypeptide chains held together by covalent disulfide bonds and non-covalent interactions. Human light chains comprise a variable domain (VL) and a constant domain (CL) wherein the constant domain may be readily classified as kappa or lambda based on amino acid sequence and gene loci. Each heavy chain comprises one variable domain (VH) and a constant region, which in the case of IgG, IgA, and IgD, comprises three domains termed CH1, CH2, and CH3 (IgM and IgE have a fourth domain, CH4). In IgG, IgA, and IgD classes the CH1 and CH2 domains are separated by a flexible hinge region, which is a proline and cysteine rich segment of variable length (generally from about 10 to about 60 amino acids in IgG). The variable domains in both the light and heavy chains are joined to the constant domains by a “J” region of about 12 or more amino acids and the heavy chain also has a “D” region of about 10 additional amino acids. Each class of antibody further comprises inter-chain and intra-chain disulfide bonds formed by paired cysteine residues. There are two types of native disulfide bridges or bonds in immunoglobulin molecules: interchain and intrachain disulfide bonds. The location and number of interchain disulfide bonds vary according to the immunoglobulin class and species. Interchain disulfide bonds are located on the surface of the immunoglobulin, are accessible to solvent and are usually relatively easily reduced. In the human IgG1 isotype there are four interchain disulfide bonds, one from each heavy chain to the light chain and two between the heavy chains. The interchain disulfide bonds are not required for chain association. As is well known the cysteine rich IgG1 hinge region of the heavy chain has generally been held to consist of three parts: an upper hinge, a core hinge, and a lower hinge. Those skilled in the art will appreciate that that the IgG1 hinge region contain the cysteines in the heavy chain that comprise the interchain disulfide bonds (two heavy/heavy, two heavy/light), which provide structural flexibility that facilitates Fab movements. The interchain disulfide bond between the light and heavy chain of IgG1 are formed between C214 of the kappa or lambda light chain and C220 in the upper hinge region of the heavy chain. The interchain disulfide bonds between the heavy chains are at positions C226 and C229 (all numbered per the EU index according to Kabat, et al., infra.)

As used herein the term “antibody” includes polyclonal antibodies, multiclonal antibodies, monoclonal antibodies, chimeric antibodies, deimmunized, humanized and primatized antibodies, CDR grafted antibodies, human antibodies, recombinantly produced antibodies, intrabodies, multispecific antibodies, bispecific antibodies, monovalent antibodies (e.g., a monovalent IgG), multivalent antibodies, anti-idiotypic antibodies, synthetic antibodies, including muteins and variants thereof, immunospecific antibody fragments such as: hcIgG, a V-NAR, Fv, Fd, Fab, F(ab′)2, F(ab′), Fab2, Fab3 fragments, single-chain fragments (e.g., di-scFv, scFv, scFvFc, scFv-zipper, scFab), disulfide-linked Fvs (sdFv), a Fd fragment consisting of the VH and CH1 domains, linear antibodies, single domain antibodies such as nanobodies or single variable domain antibodies comprising merely one variable domain such as sdAb (VH, VL, or VHH domains), “r IgG” (“half antibody”), diabodies, single chain diabodies, tandem diabodies (Tandab's), tandem di-scFv, tandem tri-scFv, “minibodies” are in some instances exemplified by a structure which is as follows: (VH-VL-CH3)2, (scFv-CH3)2, ((scFv)2-CH3+CH3), ((scFv)2-CH3) or (scFv-CH3-scFv)2, multibodies such as triabodies or tetrabodies; and derivatives thereof including Fc fusions and other modifications, and any other immunoreactive molecule so long as it comprises a domain having a binding site for preferential association or binding with an FLT3 protein. Moreover, unless dictated otherwise by contextual constraints the term further comprises all classes of antibodies (i.e. IgA, IgD, IgE, IgG, and IgM) and all subclasses (i.e., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2). Heavy-chain constant domains that correspond to the different classes of antibodies are typically denoted by the corresponding lower case Greek letter alpha, delta, epsilon, gamma, and mu, respectively. Light chains of the antibodies from any vertebrate species can be assigned to one of two clearly distinct types, called kappa (kappa) and lambda (lambda), based on the amino acid sequences of their constant domains.

In some embodiments, the FLT3 binding proteins comprise a heavy chain only antibody, such as a VH or a VHH domain. In some cases, the FLT3 binding proteins comprise a heavy chain only antibody that is an engineered human VH domain. In some examples, the engineered human VH domain is produced by panning of phage display libraries. In some embodiments, the FLT3 binding proteins comprise a VHH. The term “VHH,” as used herein, refers to single chain antibody binding domain devoid of light chain. In some cases, a VHH is derived from an antibody of the type that can be found in Camelidae or cartilaginous fish which are naturally devoid of light chains or to a synthetic and non-immunized VHH which can be constructed accordingly. Each heavy chain comprises a variable region encoded by V-, D- and J exons. A VHH, in some cases, is a natural VHH, such as a Camelid-derived VHH, or a recombinant protein comprising a heavy chain variable domain. In some embodiments, the VHH is derived from a species selected from the group consisting of camels, llamas, vicunas, guanacos, and cartilaginous fish (such as, but not limited to, sharks). In another embodiment, the VHH is derived from an alpaca (such as, but not limited to, a Huacaya Alpaca or a Suri alpaca).

As used herein, “Variable region” or “variable domain” refers to the fact that certain portions of the variable domains differ extensively in sequence among antibodies and are used in the binding and specificity of each particular antibody for its particular antigen. However, the variability is not evenly distributed throughout the variable domains of antibodies. It is concentrated in three segments called complementarity-determining regions (CDRs) or hypervariable regions both in the light-chain and the heavy-chain variable domains. The more highly conserved portions of variable domains are called the framework (FR). The variable domains of native heavy and light chains each comprise four FR regions, largely adopting a β-sheet configuration, connected by three CDRs, which form loops connecting, and in some cases forming part of, the βsheet structure. The CDRs in each chain are held together in close proximity by the FR regions and, with the CDRs from the other chain, contribute to the formation of the antigen-binding site of antibodies (see Kabat et al., Sequences of Proteins of Immunological Interest, Fifth Edition, National Institute of Health, Bethesda, Md. (1991)). The constant domains are not involved directly in binding an antibody to an antigen, but exhibit various effector functions, such as participation of the antibody in antibody-dependent cellular toxicity. The assignment of amino acids to each domain, framework region and CDR is, in some embodiments, in accordance with one of the numbering schemes provided by Kabat et al. (1991) Sequences of Proteins of Immunological Interest (5th Ed.), US Dept. of Health and Human Services, PHS, NIH, NIH Publication no. 91-3242; Chothia et al., 1987, PMID: 3681981; Chothia et al., 1989, PMID: 2687698; MacCallum et al., 1996, PMID: 8876650; or Dubel, Ed. (2007) Handbook of Therapeutic Antibodies, 3rd Ed., Wily-VCH Verlag GmbH and Co or AbM (Oxford Molecular/MSI Pharmacopeia) unless otherwise noted. In some embodiments of this disclosure, the FLT3 binding proteins comprise heavy chain only antibodies, such as VH or VHH domains, and comprise three CDRs. Such heavy chain only antibodies, in some embodiments, bind FLT3 as a monomer with no dependency on dimerisation with a VL (light chain variable) region for optimal binding affinity.

“Variable domain residue numbering as in Kabat” or “amino acid position numbering as in Kabat,” and variations thereof, refers to the numbering system used for heavy chain variable domains or light chain variable domains of the compilation of antibodies in Kabat et al., Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, Md. (1991). Using this numbering system, the actual linear amino acid sequence may contain fewer or additional amino acids corresponding to a shortening of, or insertion into, a FR or CDR of the variable domain. For example, a heavy chain variable domain may include a single amino acid insert (residue 52a according to Kabat) after residue 52 of H2 and inserted residues (e.g., residues 82a, 82b, and 82c, etc. according to Kabat) after heavy chain FR residue 82. The Kabat numbering of residues may be determined for a given antibody by alignment at regions of homology of the sequence of the antibody with a “standard” Kabat numbered sequence. It is not intended that CDRs of the present disclosure necessarily correspond to the Kabat numbering convention.

The term “Framework” or “FR” residues (or regions) refer to variable domain residues other than the CDR or hypervariable region residues as herein defined. A “human consensus framework” is a framework which represents the most commonly occurring amino acid residue in a selection of human immunoglobulin VL or VH framework sequences.

The term “epitope,” as used herein, refers to an antigenic determinant that interacts with a specific antigen binding site in the variable region of an antibody molecule known as a paratope. A single antigen may have more than one epitope. Thus, different antibodies may bind to different areas on an antigen and may have different biological effects. Epitopes may be either conformational or linear. A conformational epitope is produced by spatially juxtaposed amino acids from different segments of the linear polypeptide chain. A linear epitope is one produced by adjacent amino acid residues in a polypeptide chain. In certain circumstance, an epitope may include moieties of saccharides, phosphoryl groups, or sulfonyl groups on the antigen.

As used herein, the term “Percent (%) amino acid sequence identity” with respect to a sequence is defined as the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the specific sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity, and not considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent amino acid sequence identity can be achieved in various ways that are within the skill in the art, for instance, using publicly available computer softwares such as EMBOSS MATCHER, EMBOSS WATER, EMBOSS STRETCHER, EMBOSS NEEDLE, EMBOSS LALIGN, BLAST, BLAST-2, ALIGN or Megalign (DNASTAR) software. Those skilled in the art can determine appropriate parameters for measuring alignment, including any algorithms needed to achieve maximal alignment over the full length of the sequences being compared. Alignment for purposes of determining percent amino acid sequence identity can for example be achieved using publicly available sequence comparison computer program ALIGN-2. The source code for the ALIGN-2 sequence comparison computer program is available with user documentation in the U.S. Copyright Office, Washington D.C., 20559, where it is registered under U.S. Copyright Registration No. TXU510087. The ALIGN-2 program can be compiled for use on a UNIX operating system, such as a digital UNIX V4.0D. All sequence comparison parameters are set by the ALIGN-2 program and do not vary.

As used herein, “elimination half-time” is used in its ordinary sense, as is described in Goodman and Gillman's The Pharmaceutical Basis of Therapeutics 21-25 (Alfred Goodman Gilman, Louis S. Goodman, and Alfred Gilman, eds., 6th ed. 1980). Briefly, the term is meant to encompass a quantitative measure of the time course of drug elimination. The elimination of most drugs is exponential (i.e., follows first-order kinetics), since drug concentrations usually do not approach those required for saturation of the elimination process. The rate of an exponential process may be expressed by its rate constant, k, which expresses the fractional change per unit of time, or by its half-time, tin, the time required for 50% completion of the process. The units of these two constants are time-1 and time, respectively. A first-order rate constant and the half-time of the reaction are simply related (k×t_(1/2)=0.693) and may be interchanged accordingly. Since first-order elimination kinetics dictates that a constant fraction of drug is lost per unit time, a plot of the log of drug concentration versus time is linear at all times following the initial distribution phase (i.e., after drug absorption and distribution are complete). The half-time for drug elimination can be accurately determined from such a graph.

As used herein, the term “binding affinity” refers to the affinity of the proteins described in the disclosure to their binding targets, and is expressed numerically using “Kd” values. If two or more proteins are indicated to have comparable binding affinities towards their binding targets, then the Kd values for binding of the respective proteins towards their binding targets, are within ±2-fold of each other. If two or more proteins are indicated to have comparable binding affinities towards single binding target, then the Kd values for binding of the respective proteins towards said single binding target, are within ±2-fold of each other. If a protein is indicated to bind two or more targets with comparable binding affinities, then the Kd values for binding of said protein to the two or more targets are within ±2-fold of each other. In general, a higher Kd value corresponds to a weaker binding. In some embodiments, the “Kd” is measured by a radiolabeled antigen binding assay (MA) or surface plasmon resonance assays using a BIAcore™-2000 or a BIAcore™-3000 (BIAcore, Inc., Piscataway, N.J.). In certain embodiments, an “on-rate” or “rate of association” or “association rate” or “kon” and an “off-rate” or “rate of dissociation” or “dissociation rate” or “koff” are also determined with the surface plasmon resonance technique using a BIAcore™-2000 or a BIAcore™-3000 (BIAcore, Inc., Piscataway, N.J.). In additional embodiments, the “Kd”, “kon”, and “koff” are measured using the OCTET® Systems (Pall Life Sciences). In an exemplary method for measuring binding affinity using the OCTET® Systems, the ligand, e.g., biotinylated human or cynomolgus FLT3, is immobilized on the OCTET® streptavidin capillary sensor tip surface which streptavidin tips are then activated according to manufacturer's instructions using about 20-50 μg/ml human or cynomolgus FLT3 protein. A solution of PBS/Casein is also introduced as a blocking agent. For association kinetic measurements, FLT3 binding protein variants are introduced at a concentration ranging from about 10 ng/mL to about 100 μg/mL, about 50 ng/mL to about 5 μg/mL, or about 2 ng/mL to about 20 μg/mL. In some embodiments, the FLT3 binding single domain proteins are used at a concentration ranging from about 2 ng/mL to about 20 μg/mL. Complete dissociation is observed in case of the negative control, assay buffer without the binding proteins. The kinetic parameters of the binding reactions are then determined using an appropriate tool, e.g., ForteBio software.

As used herein, in some embodiments, “treatment” or “treating” or “treated” refers to therapeutic treatment wherein the object is to slow (lessen) an undesired physiological condition, disorder or disease, or to obtain beneficial or desired clinical results. For the purposes described herein, beneficial or desired clinical results include, but are not limited to, alleviation of symptoms; diminishment of the extent of the condition, disorder or disease; stabilization (i.e., not worsening) of the state of the condition, disorder or disease; delay in onset or slowing of the progression of the condition, disorder or disease; amelioration of the condition, disorder or disease state; and remission (whether partial or total), whether detectable or undetectable, or enhancement or improvement of the condition, disorder or disease. Treatment includes eliciting a clinically significant response without excessive levels of side effects. Treatment also includes prolonging survival as compared to expected survival if not receiving treatment. In other embodiments, “treatment” or “treating” or “treated” refers to prophylactic measures, wherein the object is to delay onset of or reduce severity of an undesired physiological condition, disorder or disease, such as, for example is a person who is predisposed to a disease (e.g., an individual who carries a genetic marker for a disease such as breast cancer).

An “FLT3 targeting TriTAC,” or an “FLT3 targeting trispecific protein,” as used herein refers to a trispecific binding protein that comprises a binding moiety that is specific for a bulk serum protein, a first target antigen binding domain, and a second target antigen binding domain, wherein at least one of the first target antigen binding domain and the second target antigen binding domain comprises an FLT3 binding protein as described herein, and at least one of the first target antigen binding domain and the second target antigen binding domain comprises a domain that binds a CD3.

A “ProTriTAC,” or an “FLT3 targeting protrispecific protein,” as used herein refers to a trispecific binding protein that is conditionally activated, and comprises (i) a cleavable linker; (ii) a dual binding moiety that is specific for a bulk serum protein and also comprises a masking moiety which prohibits the binding of a first target antigen binding domain or a second target antigen binding domain to its target, wherein at least one of the first target antigen binding domain and the second target antigen binding domain comprises an FLT3 binding domain as described herein. The ProTriTAC proteins of this disclosure are, in some cases, activated from a masked state to an active state by cleavage of the cleavable linker, for example, in a protease rich environment, such as in a tumor microenvironment.

FLT3 Binding Proteins

FLT3, also known as fetal liver kinase 2 (FLK-2), stem cell tyrosine kinase 1 (STK-1) and CD135, is a member of the class III receptor tyrosine kinases. Normally, FLT3 is expressed on immature myeloid-lymphocytic precursor cells and dendritic cell precursors, but rarely on mature adult cells. FLT3 is overexpressed in approximately 90% of acute myeloid leukemia (AML), a majority of acute lymphocytic leukemia (ALL) and the blast-crisis phase of chronic myeloid leukemia (BC-CIVIL). Stimulation by FLT3 ligand (FL) enhances the proliferation and survival of leukemia cells. Inhibition of FLT3 signaling leads to apoptosis in dendritic cells and inhibition of immune responses. The MAPK, PI3K and Stat5 pathways have been identified to be involved in the downstream signaling of activated FLT3 (See e.g., Stirewalt D L and J P, Radich, J P. Nat Rev Cancer 3:650-665 (2003)).

Described herein are proteins that comprise an FLT3 binding domain, pharmaceutical compositions thereof, as well as nucleic acids, recombinant expression vectors and host cells for making such proteins thereof. Also provided are methods of using the disclosed proteins comprising an FLT3 binding domain of this disclosure, in the prevention, and/or treatment of diseases, conditions and disorders. In some embodiments, an FLT3 binding domain of this disclosure inhibits FL-induced phosphorylation of wild-type FLT3 and downstream kinases of MPK, PI3K, and STATS pathways in a disease such as leukemia. In some embodiments, an FLT3 binding domain of this disclosure has an improved ability to activate downstream immune effector functions such as antibody dependent cellular cytotoxicity (ADCC).

In some embodiments, the FLT3 binding domain binds to a human FLT3 protein comprising a sequence as set forth in SEQ ID No. 388 (UniProt ID: P36888). In some embodiments, the FLT3 binding domain binds to a protein comprising a truncated sequence compared to SEQ ID No. 388 (UniProt ID: P36888).

In some embodiments, the FLT3 binding domains disclosed herein recognize full-length FLT3 (e.g., an FLT3 protein comprising the sequence of SEQ ID No. 388 (UniProt ID: P36888). In certain instances, the FLT3 binding domains disclosed herein recognize an epitope within FLT3, such as, in some cases the FLT3 binding proteins interact with one or more amino acids found within a domain of human FLT3. The epitope to which the antibodies bind may consist of a single contiguous sequence of 3 or more (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more) amino acids located within a domain of FLT3 (e.g., an FLT3 protein comprising the sequence of SEQ ID No. 388 (UniProt ID: P36888). Alternatively, the epitope may consist of a plurality of non-contiguous amino acids (or amino acid sequences) located within a domain of FLT3 (e.g., an FLT3 protein comprising the sequence of SEQ ID No. 388 (UniProt ID: P36888).

In some embodiments, the FLT3 binding proteins of this disclosure binds to the full length of an FLT3 protein or to a fragment thereof, such as epitope containing fragments within the full length FLT3 protein, as described above. In some cases, the epitope containing fragment comprises antigenic or immunogenic fragments and derivatives thereof of the FLT3 protein. Epitope containing fragments, including antigenic or immunogenic fragments, are, in some embodiments, 12 amino acids or more, e.g., 20 amino acids or more, 50 or 100 amino acids or more. The FLT3 fragments, in some embodiments, comprises 95% or more of the length of the full protein, 90% or more, 75% or 50% or 25% or 10% or more of the length of the full protein. In some embodiments, the epitope-containing fragments of FLT3 including antigenic or immunogenic fragments are capable of eliciting a relevant immune response in a patient. Derivatives of FLT3 include, in some embodiments, variants on the sequence in which one or more (e.g., 1-20 such as 15 amino acids, or up to 20% such as up to 10% or 5% or 1% by number of amino acids based on the total length of the protein) deletions, insertions or substitutions have been made to the FLT3 sequence (e.g., an FLT3 protein comprising the sequence of SEQ ID No. 388 (UniProt ID: P36888).

In some embodiments, substitutions comprise conservative substitutions. Derivatives and variants of, in some examples, have essentially the same biological function as the protein from which they are derived. For instance, derivatives and variants of FLT3 are, in some cases, comparably antigenic or immunogenic to the protein from which they are derived, have either the ligand-binding activity, or the active receptor-complex forming ability, or preferably both, of the protein from which they are derived, and have the same tissue distribution as FLT3.

In some embodiments, the FLT3 binding protein specifically binds FLT3 with equivalent or better affinity as that of a reference FLT3 binding protein, and the FLT3 binding protein in such embodiments comprises an affinity matured FLT3 binding molecule, and is derived from the FLT3 binding parental molecule, comprising one or more amino acid mutations (e.g., a stabilizing mutation, a destabilizing mutation) with respect to the FLT3 binding parental molecule. In some embodiments, the affinity matured FLT3 binding molecule has superior stability with respect to selected destabilizing agents, as that of a reference FLT3 binding parental molecule. In some embodiments, the affinity matured FLT3 binding molecule is identified in a process comprising panning of one or more pre-candidate FLT3 binding molecules derived from one or more FLT3 binding parental molecule, expressed in a phage display library, against an FLT3 protein, such as a human FLT3 protein. The pre-candidate FLT3 binding molecule comprises, in some embodiments, amino acid substitutions in the variable regions, CDRs, or framework residues, relative to a parental molecule.

As used herein, “Phage display,” refers to a technique by which variant polypeptides are displayed as fusion proteins to at least a portion of a coat protein on the surface of phage, e.g., filamentous phage, particles. A utility of phage display lies in the fact that large libraries of randomized protein variants can be rapidly and efficiently selected for those sequences that bind to a target molecule with high affinity. Display of peptide and protein libraries on phage has been used for screening millions of polypeptides for ones with specific binding properties. Polyvalent phage display methods have been used for displaying small random peptides and small proteins through fusions to either gene III or gene VIII of filamentous phage. See e.g., Wells and Lowman, Curr. Opin. Struct. Biol, 3:355-362 (1992), and references cited therein. In monovalent phage display, a protein or peptide library is fused to a gene III or a portion thereof, and expressed at low levels in the presence of wild type gene III protein so that phage particles display one copy or none of the fusion proteins. Avidity effects are reduced relative to polyvalent phage so that selection is on the basis of intrinsic ligand affinity, and phagemid vectors are used, which simplify DNA manipulations. See e.g., Lowman and Wells, Methods: A companion to Methods in Enzymology, 3:205-0216 (1991).

In some embodiments, the panning comprises using varying binding times and concentrations to identify FLT3 binding molecules with increased or decreased on-rates, from pre-candidate FLT3 binding molecules. In some embodiments, the panning comprises using varying wash times to identify FLT3 binding molecules with increased or decreased off-rates, from pre-candidate FLT3 molecules. In some embodiments, the panning comprises using both varying binding times and varying wash times. In some embodiments, one or more stabilizing mutations are combined to increase the stability of the affinity matured FLT3 binding molecule, for example, by shuffling to create a second-stage combinatorial library from such mutants and conducting a second round of panning followed by a binding selection.

In some embodiments, the affinity matured FLT3 binding molecule comprises an equivalent or better affinity to a FLT3 protein (such as human FLT3 protein) as that of a FLT3 binding parental molecule, but that has reduced cross reactivity, or in some embodiments, increased cross reactivity, with selected substances, such as ligands, proteins, antigens, or the like, other than the FLT3 epitope for which the FLT3 binding parental molecule is specific, or is designed to be specific for. In regard to the latter, an affinity matured FLT3 binding molecule, in some embodiments, is more successfully tested in animal models if the affinity matured FLT3 binding molecule is reacted with both human FLT3 and the corresponding target of the animal model, e.g. mouse FLT3 or cynomolgus FLT3.

In some embodiments, the FLT3 binding protein comprises an antigen-specific binding domain polypeptide that specifically bind to targets, such as targets on diseased cells, or targets on other cells that support the diseased state, such as targets on stromal cells that support tumor growth or targets on immune cells that support disease-mediated immunosuppression. In some examples, the antigen-specific binding domain includes antibodies, single chain antibodies, Fabs, Fv, T-cell receptor binding domains, ligand binding domains, receptor binding domains, domain antibodies, single domain antibodies, minibodies, nanobodies, peptibodies, or various other antibody mimics (such as affimers, affitins, alphabodies, atrimers, CTLA4-based molecules, adnectins, anticalins, Kunitz domain-based proteins, avimers, knottins, fynomers, darpins, affibodies, affilins, monobodies and armadillo repeat protein-based proteins).

In some embodiments, the FLT3 binding domain is an anti-FLT3 antibody or an antigen binding fragment thereof, or a variant of the anti-FLT3 or an antigen binding fragment thereof. As used herein, the term “variant” refers to variants and derivatives of an antibody or an antigen binding fragment thereof, as described herein. In certain embodiments, amino acid sequence variants of the anti-FLT3 antibodies or antigen binding fragments thereof described herein are contemplated. For example, in certain embodiments amino acid sequence variants of anti-FLT3 antibodies or antigen binding fragments thereof described herein are contemplated to improve the binding affinity and/or other biological properties of the same. Exemplary method for preparing amino acid variants include, but are not limited to, introducing appropriate modifications into the nucleotide sequence encoding the antibody or antigen binding fragments thereof, or by peptide synthesis. Such modifications include, for example, deletions from, and/or insertions into and/or substitutions of residues within the amino acid sequences of the antibody or antigen binding fragments thereof.

Any combination of deletion, insertion, and substitution can be made to arrive at the final construct, provided that the final construct possesses the desired characteristics, e.g., antigen-binding. In certain embodiments, variants having one or more amino acid substitutions are provided. Sites of interest for substitution mutagenesis include the CDRs and framework regions. Examples of such substitutions are described below. Amino acid substitutions may be introduced into an antibody or antigen binding fragments thereof of interest and the products screened for a desired activity, e.g., retained/improved antigen binding, decreased immunogenicity, altered Antibody dependent cellular cytotoxicity (ADCC), or improved T-cell mediated cytotoxicity (TDCC). Both conservative and non-conservative amino acid substitutions are contemplated for preparing the variants.

In another example of a substitution to create a variant anti-FLT3 antibody or antigen binding fragments thereof, one or more hypervariable region residues of a parent antibody or antigen binding fragments thereof are substituted. In general, variants are then selected based on improvements in desired properties compared to a parent antibody, for example, increased affinity, reduced affinity, reduced immunogenicity, increased pH dependence of binding.

In some embodiments, the FLT3 binding domain is a single domain antibody (sdAb), such as a heavy chain variable domain (VH), a variable domain (VHH) of a llama derived sdAb, a peptide, a ligand or a small molecule entity specific for FLT3. In some embodiments, the FLT3 binding domain described herein is any domain that binds to FLT3 including but not limited to domains from a monoclonal antibody, a polyclonal antibody, a recombinant antibody, a human antibody, a humanized antibody. In certain embodiments, the FLT3 binding domain is a single-domain antibody. In other embodiments, the FLT3 binding domain is a peptide. In further embodiments, the FLT3 binding domain is a small molecule.

Generally, it should be noted that the term single domain antibody as used herein in its broadest sense is not limited to a specific biological source or to a specific method of preparation. Single domain antibodies are antibodies whose complementary determining regions are part of a single domain polypeptide. Examples include, but are not limited to, heavy chain antibodies, antibodies naturally devoid of light chains, single domain antibodies derived from conventional 4-chain antibodies, engineered antibodies and single domain scaffolds other than those derived from antibodies. Single domain antibodies may be any of the art, or any future single domain antibodies. Single domain antibodies may be derived from any species including, but not limited to mouse, human, camel, llama, goat, rabbit, bovine. For example, in some embodiments, the single domain antibodies of the disclosure are obtained: (1) by isolating the VHH domain of a naturally occurring heavy chain antibody; (2) by expression of a nucleotide sequence encoding a naturally occurring VHH domain; (3) by “humanization” of a naturally occurring VHH domain or by expression of a nucleic acid encoding a such humanized VHH domain; (4) by “camelization” of a naturally occurring VH domain from any animal species, and in particular from a species of mammal, such as from a human being, or by expression of a nucleic acid encoding such a camelized VH domain; (5) by “camelization” of a “domain antibody” or “Dab,” or by expression of a nucleic acid encoding such a camelized VH domain; (6) by using synthetic or semi-synthetic techniques for preparing proteins, polypeptides or other amino acid sequences; (7) by preparing a nucleic acid encoding a single domain antibody using techniques for nucleic acid synthesis known in the field, followed by expression of the nucleic acid thus obtained; and/or (8) by any combination of one or more of the foregoing.

In one embodiment, a single domain antibody corresponds to the VHH domains of naturally occurring heavy chain antibodies directed against FLT3. As further described herein, such VHH sequences can generally be generated or obtained by suitably immunizing a species of Llama with FLT3, (i.e., so as to raise an immune response and/or heavy chain antibodies directed against FLT3), by obtaining a suitable biological sample from said Llama (such as a blood sample, serum sample or sample of B-cells), and by generating VHH sequences directed against FLT3, starting from said sample, using any suitable technique.

In another embodiment, such naturally occurring VHH domains against FLT3, are obtained from naïve libraries of Camelid VHH sequences, for example by screening such a library using FLT3, or at least one part, fragment, antigenic determinant or epitope thereof using one or more screening techniques known in the field. Such libraries and techniques are for example described in WO 99/37681, WO 01/90190, WO 03/025020 and WO 03/035694. Alternatively, improved synthetic or semi-synthetic libraries derived from naïve VHH libraries are used, such as VHH libraries obtained from naïve VHH libraries by techniques such as random mutagenesis and/or CDR shuffling, as for example described in WO 00/43507.

In a further embodiment, yet another technique for obtaining VHH sequences directed against FLT3, involves suitably immunizing a transgenic mammal that is capable of expressing heavy chain antibodies (i.e., so as to raise an immune response and/or heavy chain antibodies directed against FLT3), obtaining a suitable biological sample from said transgenic mammal (such as a blood sample, serum sample or sample of B-cells), and then generating VHH sequences directed against FLT3, starting from said sample, using any suitable technique known in the field. For example, for this purpose, the heavy chain antibody-expressing rats or mice and the further methods and techniques described in WO 02/085945 and in WO 04/049794 can be used.

In some embodiments, an anti-FLT3 single domain antibody of this disclosure comprises a single domain antibody with an amino acid sequence that corresponds to the amino acid sequence of a non-human antibody and/or a naturally occurring VHH domain, e.g., a llama anti-FLT3 antibody, but that has been “humanized,” i.e., by replacing one or more amino acid residues in the amino acid sequence of said non-human anti-FLT3 and/or the naturally occurring VHH sequence (and in particular in the framework sequences) by one or more of the amino acid residues that occur at the corresponding position(s) in a VH domain from a conventional 4-chain antibody from a human being (e.g., as indicated above). This can be performed in a manner known in the field, which will be clear to the skilled person, for example on the basis of the further description herein. Again, it should be noted that such humanized anti-FLT3 single domain antibodies of the disclosure are obtained in any suitable manner known per se (i.e., as indicated under points (1)-(8) above) and thus are not strictly limited to polypeptides that have been obtained using a polypeptide that comprises a non-human anti-FLT3 antibody and/or the naturally occurring VHH sequence as a starting material. In some additional embodiments, a single domain anti-FLT3 antibody, as described herein, comprises a single domain antibody with an amino acid sequence that corresponds to the amino acid sequence of a naturally occurring VH domain, but that has been “camelized” i.e., by replacing one or more amino acid residues in the amino acid sequence of a naturally occurring VH domain from a conventional 4-chain antibody by one or more of the amino acid residues that occur at the corresponding position(s) in a VHH domain of a heavy chain antibody. Such “camelizing” substitutions are preferably inserted at amino acid positions that form and/or are present at the VH-VL interface, and/or at the so-called Camelidae hallmark residues. See e.g., WO 94/04678 and Davies and Riechmann (1994 and 1996)). Preferably, the VH sequence that is used as a starting material or starting point for generating or designing the camelized single domain is preferably a VH sequence from a mammal, more preferably the VH sequence of a human being, such as a VH3 sequence. However, it should be noted that such camelized anti-FLT3 single domain antibodies of the disclosure, in certain embodiments, are obtained in any suitable manner known in the field (i.e., as indicated under points (1)-(8) above) and thus are not strictly limited to polypeptides that have been obtained using a polypeptide that comprises a naturally occurring VH domain as a starting material. For example, as further described herein, both “humanization” and “camelization” is performed by providing a nucleotide sequence that encodes a naturally occurring VHH domain or VH domain, respectively, and then changing, one or more codons in said nucleotide sequence in such a way that the new nucleotide sequence encodes a “humanized” or “camelized” single domain antibody, respectively. This nucleic acid can then be expressed, so as to provide a desired anti-FLT3 single domain antibody of the disclosure. Alternatively, in other embodiments, based on the amino acid sequence of a naturally occurring VHH domain or VH domain, respectively, the amino acid sequence of the desired humanized or camelized anti-FLT3 single domain antibody of the disclosure, respectively, are designed and then synthesized de novo using known techniques for peptide synthesis. In some embodiments, based on the amino acid sequence or nucleotide sequence of a naturally occurring VHH domain or VH domain, respectively, a nucleotide sequence encoding the desired humanized or camelized anti-FLT3 single domain antibody of the disclosure, respectively, is designed and then synthesized de novo using known techniques for nucleic acid synthesis, after which the nucleic acid thus obtained is expressed in using known expression techniques, so as to provide the desired anti-FLT3 single domain antibody of the disclosure.

Other suitable methods and techniques for obtaining the anti-FLT3 single domain antibody of the disclosure and/or nucleic acids encoding the same, starting from naturally occurring VH sequences or VHH sequences for example comprises combining one or more parts of one or more naturally occurring VH sequences (such as one or more framework (FR) sequences and/or complementarity determining region (CDR) sequences), one or more parts of one or more naturally occurring VHH sequences (such as one or more FR sequences or CDR sequences), and/or one or more synthetic or semi-synthetic sequences, in a suitable manner, so as to provide an anti-FLT3 single domain antibody of the disclosure or a nucleotide sequence or nucleic acid encoding the same.

In some embodiments, the FLT3 binding domain is an anti-FLT3 specific antibody comprising a heavy chain variable complementarity determining region CDR1, a heavy chain variable CDR2, a heavy chain variable CDR3, a light chain variable CDR1, a light chain variable CDR2, and a light chain variable CDR3. In some embodiments, the FLT3 binding domain comprises any domain that binds to FLT3 including but not limited to domains from a monoclonal antibody, a polyclonal antibody, a recombinant antibody, a human antibody, a humanized antibody, or antigen binding fragments such as single domain antibodies (sdAb), Fab, Fab′, F(ab)2, and Fv fragments, fragments comprised of one or more CDRs, single-chain antibodies (e.g., single chain Fv fragments (scFv)), disulfide stabilized (dsFv) Fv fragments, heteroconjugate antibodies (e.g., bispecific antibodies), pFv fragments, heavy chain monomers or dimers, light chain monomers or dimers, and dimers consisting of one heavy chain and one light chain. In some embodiments, the FLT3 binding domain is a single domain antibody. In some embodiments, the anti-FLT3 single domain antibody comprises heavy chain variable complementarity determining regions (CDR), CDR1, CDR2, and CDR3.

In some embodiments, the FLT3 binding domain is a polypeptide comprising an amino acid sequence that is comprised of four framework regions/sequences (f1-f4) interrupted by three complementarity determining regions/sequences, as represented by the formula: f1-r1-f2-r2-f3-r3-f4, wherein r1, r2, and r3 are complementarity determining regions CDR1, CDR2, and CDR3, respectively, and f1, f2, f3, and f4 are framework residues. The framework residues of the FLT3 binding protein of the present disclosure comprise, for example, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, or 94 amino acid residues, and the complementarity determining regions comprise, for example, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, or 36 amino acid residues.

In some embodiments, the binding proteins described herein comprise a polypeptide having a sequence selected from SEQ ID Nos. 1-76, and 389-390, subsequences thereof, and variants thereof. In some embodiments, the FLT3 binding protein comprises at least 60%-95% or more homology to a sequence selected from SEQ ID Nos. 1-76, and 389-390, subsequences thereof, and variants thereof. In some embodiments, the FLT3 binding protein comprises at least 60%, 61%, 62%, 63%, 63%, 65%, 66%, 67%, 68%, 69%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or more homology to a sequence selected from SEQ ID Nos. 1-76, and 389-390, subsequences thereof, and variants thereof. In some embodiments, the FLT3 binding protein comprises at least 60%-95% or more identity to a sequence selected from SEQ ID Nos. 1-76, and 389-390, subsequences thereof, and variants thereof. In some embodiments, the FLT3 binding protein comprises at least 60%, 61%, 62%, 63%, 63%, 65%, 66%, 67%, 68%, 69%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or more identity to a sequence selected from SEQ ID Nos. 1-76, and 389-390, subsequences thereof, and variants thereof.

In some embodiments, the CDR1 comprises the amino acid sequence selected from the group consisting of SEQ ID Nos. 77-108 or a sequence comprising one or more amino acid substitutions in a sequence selected from the group consisting of SEQ ID Nos. 77-108. In some embodiments, the CDR2 comprises the amino acid sequence selected from the group consisting of SEQ ID Nos. 109-154, and 393-394 or a sequence comprising one or more amino acid substitutions in a sequence selected from the group consisting of SEQ ID Nos. 109-154, and 393-394. In some embodiments, the CDR3 comprises the amino acid sequence selected from the group consisting of SEQ ID Nos. 155-195 or a sequence comprising one or more amino acid substitutions in a sequence selected from the group consisting of SEQ ID Nos. 155-195. In some embodiments, the CDR1 comprises the amino acid sequence selected from the group consisting of SEQ ID Nos. 89, 91, 92, 93, and 100 or a sequence comprising one or more amino acid substitutions in a sequence selected from the group consisting of SEQ ID Nos. 89, 91, 92, 93, and 100. In some embodiments, the CDR2 comprises the amino acid sequence selected from the group consisting of SEQ ID Nos. 149, 150, 151, 152, 153, 154, 393 and 394, or a sequence comprising one or more amino acid substitutions in a sequence selected from the group consisting of SEQ ID Nos. 149, 150, 151, 152, 153, 154, 393 and 394. In some embodiments, the CDR3 comprises the amino acid sequence selected from the group consisting of SEQ ID Nos. 173, 186 or 195 or a sequence comprising one or more amino acid substitutions in a sequence selected from the group consisting of SEQ ID Nos. 173, 196 or 195.

In various embodiments, the FLT3 binding domain of the present disclosure is at least about 60%, about 61%, at least about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to an amino acid sequence selected from SEQ ID Nos. 1-76, and 389-390.

In various embodiments, the FLT3 binding domain of the present disclosure is at least about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to an amino acid sequence selected from SEQ ID Nos.1-76, and 389-390.

In various embodiments, a complementarity determining region of the FLT3 binding domain of the present disclosure is at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to the amino acid sequence set forth in any one of SEQ ID Nos. 77-108.

In various embodiments, a complementarity determining region of the FLT3 binding domain of the present disclosure is at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to the amino acid sequence set forth in SEQ ID Nos. 109-154, and 393-394.

In various embodiments, a complementarity determining region of the FLT3 binding domain of the present disclosure is at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to the amino acid sequence set forth in SEQ ID Nos. 155-195.

In various embodiments, a complementarity determining region of the FLT3 binding domain of the present disclosure is at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to the amino acid sequence set forth in any one of SEQ ID Nos. 89, 91, 92, 93, and 100, and wherein the FLT3 binding domain comprises a humanized FLT3 binding domain.

In various embodiments, a complementarity determining region of the FLT3 binding domain of the present disclosure is at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to the amino acid sequence set forth in any one of SEQ ID Nos. 149, 150, 151, 152, 153, and 154, and wherein the FLT3 binding domain comprises a humanized FLT3 binding domain.

In various embodiments, a complementarity determining region of the FLT3 binding domain of the present disclosure is at least about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, or about 100% identical to the amino acid sequence set forth in any one of SEQ ID Nos. 173, 186 and 195, and wherein the FLT3 binding domain comprises a humanized FLT3 binding domain.

In some embodiments, the FLT3 binding domains of this disclosure comprises a set of three CDR sequences, as provided in Table 1.

TABLE 1 CDR sequences of exemplary FLT3 binding domains of this disclosure FLT3 Binder CDR1 CDR2 CDR3 FLL101 77 109 155 FLL103 78 109 155 FLL116 77 109 155 FLL125 79 110 156 FLL129 80 111 155 FLL137 81 112 155 FLL14 77 109 155 FLL146 77 113 157 FLL158 82 110 156 FLL179 77 114 158 FLL181 80 111 155 FLL187 77 109 155 FLL32 83 115 155 FLL51 84 111 155 FLL55 79 116 156 FLL77 85 111 155 FLL97 77 109 155 FLL21 79 110 156 FLL57 86 110 156 FLL62 87 110 156 FLL79 79 110 156 FLL86 79 110 156 FLL112 88 117 159 FLL142 88 118 160 FLL143 88 119 161 FLL154 88 120 162 FLL168 88 121 163 FLL170 88 122 164 FLL188 88 121 165 FLL40 88 122 164 FLL6 88 121 166 FLL75 88 122 167 FLL83 88 122 168 FLL94 88 121 169 FLL99 88 118 165 FLL38 88 123 170 FLL53 88 124 171 FLL553 88 122 167 FLL74 88 117 172 FLL102 89 125 173 FLL122 89 125 173 FLL134 90 126 174 FLL153 90 127 175 FLL41 90 125 176 FLL67 90 125 176 FLL92 89 125 173 FLL71 90 128 175 FLL8 90 128 177 FLL84 90 125 176 FLL107 91 129 178 FLL141 91 130 178 FLL34 92 131 178 FLL4 93 132 178 FLL61 94 133 179 FLL78 91 134 178 FLL1 95 135 180 FLL26 96 136 181 FLL160 97 137 182 FLL173 97 138 183 FLL178 98 139 184 FLL27 99 139 185 FLL190 100 140 186 FLL43 101 141 187 FLL15 102 142 188 FLL45 103 143 189 FLL39 104 144 190 FLL177 105 145 191 FLL823 106 146 192 FLL76 107 147 193 FLL822 108 148 194 FLH107 91 149 195 FLH141 91 150 195 FLH19C 100 151 186 FLH34 92 152 195 FLH4 93 153 195 FLH78 91 154 195 FLH92a 89 393 173 FLH92b 89 394 173

In some embodiments, the FLT3 binding domain is cross-reactive with human cynomolgus (cyno) and mouse FLT3. In some embodiments, the FLT3 binding domain is specific for human FLT3. In certain embodiments, the FLT3 binding domains disclosed herein bind to human FLT3 with a human Kd (hKd). In certain embodiments, the FLT3 binding domains disclosed herein bind to cynomolgus FLT3 with a cyno Kd (cKd). In certain embodiments, the FLT3 binding domains disclosed herein bind to cynomolgus FLT3 with a mouse Kd (mKd). In certain embodiments, the FLT3 binding domains disclosed herein bind to both cynomolgus FLT3 and a human FLT3, with a cyno Kd (cKd) and a human Kd (hKd), respectively. In certain embodiments, the FLT3 binding domains disclosed herein bind to cynomolgus FLT3, mouse FLT3, and a human FLT3, with a cyno Kd (cKd), mouse Kd (mKd), and a human Kd (hKd), respectively. In some embodiments, the FLT3 binding protein binds to human, mouse and cynomolgus FLT3 with comparable binding affinities (i.e., hKd, mKd and cKd values do not differ by more than ±10%). In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 500 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 450 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 400 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 350 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 300 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 250 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 200 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 150 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 100 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.1 nM to about 90 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.2 nM to about 80 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.3 nM to about 70 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.4 nM to about 50 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.5 nM to about 30 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.6 nM to about 10 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.7 nM to about 8 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.8 nM to about 6 nM. In some embodiments, the hKd, mKd and the cKd range from about 0.9 nM to about 4 nM. In some embodiments, the hKd, mKd and the cKd range from about 1 nM to about 2 nM.

In some embodiments, any of the foregoing FLT3 binding domains (e.g., anti-FLT3 single domain antibodies of SEQ ID Nos. 1-76, and 389-390) are affinity peptide tagged for ease of purification. In some embodiments, the affinity peptide tag is six consecutive histidine residues, also referred to as 6×-his (SEQ ID No. 374). In certain embodiments, the FLT3 binding domains of the present disclosure preferentially bind membrane bound FLT3 over soluble FLT3 Membrane bound FLT3 refers to the presence of FLT3 in or on the cell membrane surface of a cell that expresses FLT3. Soluble FLT3 refers to FLT3 that is no longer on in or on the cell membrane surface of a cell that expresses or expressed FLT3. In certain instances, the soluble FLT3 is present in the blood and/or lymphatic circulation in a subject. In one embodiment, the FLT3 binding domains bind membrane-bound FLT3 at least 5 fold, 10 fold, 15 fold, 20 fold, 25 fold, 30 fold, 40 fold, 50 fold, 100 fold, 500 fold, or 1000 fold greater than soluble FLT3. In one embodiment, the FLT3 binding proteins of the present disclosure preferentially bind membrane-bound FLT3 30 fold greater than soluble FLT3. Determining the preferential binding of an antigen binding protein to membrane bound FLT3 over soluble FLT3 can be readily determined using binding assays.

It is contemplated that in some embodiments the FLT3 binding protein is fairly small and no more than 25 kDa, no more than 20 kDa, no more than 15 kDa, or no more than 10 kDa in some embodiments. In certain instances, the FLT3 binding protein is 5 kDa or less if it is a peptide or small molecule entity.

In other embodiments, the FLT3 binding proteins described herein comprise small molecule entity (SME) binders for FLT3. SME binders are small molecules averaging about 500 to 2000 Da in size and are attached to the FLT3 binding proteins by known methods, such as sortase ligation or conjugation. In these instances, the FLT3 binding protein comprises a domain comprising a sortase recognition sequence, e.g., LPETG (SEQ ID No. 376). To attach a SME binder to FLT3 binding protein comprising a sortase recognition sequence, the protein is incubated with a sortase and a SME binder whereby the sortase attaches the SME binder to the recognition sequence. In yet other embodiments, the FLT3 binding proteins described herein comprise a knottin peptide for binding FLT3. Knottins are disufide-stabilized peptides with a cysteine knot scaffold and have average sizes about 3.5 kDa. Knottins have been contemplated for binding to certain tumor molecules such as FLT3. In further embodiments, the FLT3 binding proteins described herein comprise a natural FLT3 ligand.

In some embodiments, the FLT3 binding protein comprises more than one domain and are of a single-polypeptide design with flexible linkage of the domains. This allows for facile production and manufacturing of the FLT3 binding proteins as they can be encoded by single cDNA molecule to be easily incorporated into a vector. Further, in some embodiments where the FLT3 binding proteins described herein are a monomeric single polypeptide chain, there are no chain pairing issues or a requirement for dimerization. It is contemplated that, in such embodiments, the FLT3 binding proteins described herein have a reduced tendency to aggregate.

In the FLT3 binding proteins comprising more than one domain, the domains are linked by one or more internal linker. In certain embodiments, the internal linkers are “short,” i.e., consist of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 amino acid residues. Thus, in certain instances, the internal linkers consist of about 12 or less amino acid residues. In the case of 0 amino acid residues, the internal linker is a peptide bond. In certain embodiments, the internal linkers are “long,” i.e., consist of 15, 20 or 25 amino acid residues. In some embodiments, the internal linkers consist of about 3 to about 15, for example 8, 9 or 10 contiguous amino acid residues. Regarding the amino acid composition of the internal linkers, peptides are selected with properties that confer flexibility to the FLT3 binding proteins, do not interfere with the binding domains as well as resist cleavage from proteases. For example, glycine and serine residues generally provide protease resistance. Examples of internal linkers suitable for linking the domains in the FLT3 binding proteins include but are not limited to (GS)n (SEQ ID No. 377), (GGS)n (SEQ ID No. 378), (GGGS)n (SEQ ID No. 379), (GGSG)n (SEQ ID No. 380), (GGSGG)n (SEQ ID No. 381), (GGGGS)n (SEQ ID No. 382), (GGGGG)n (SEQ ID No. 383), or (GGG)n (SEQ ID No. 384), wherein n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In one embodiment, the linker is (GGGGSGGGGSGGGGSGGGGS) (SEQ ID No. 385), (GGGGSGGGGSGGGGS) (SEQ ID No. 386), or (GGGGSGGGS) (SEQ ID No. 387).

In some cases, where the FLT3 binding protein comprises more than one domain, the domains within the FLT3 binding proteins are conjugated using an enzymatic site-specific conjugation method which involves the use of a mammalian or bacterial transglutaminase enzyme. Microbial transglutaminases (mTGs) are versatile tools in modern research and biotechnology. The availability of large quantities of relatively pure enzymes, ease of use, and lack of regulation by calcium and guanosine-5′-triphosphate (GTP) has propelled mTG to be the main cross-linking enzyme used in both the food industry and biotechnology. Currently, mTGs are used in many applications to attach proteins and peptides to small molecules, polymers, surfaces, DNA, as well as to other proteins. See e.g., Pavel Strp, Veracity of microbial transglutaminase, Bioconjugate Chem. 25, 5, 855-862.

In some examples are provided FLT3 binding proteins comprising more than one domain, wherein one of the domains comprises an acceptor glutamine in a constant region, which can then be conjugated to another domain via a lysine-based linker (e.g., any primary amine chain which is a substrate for TGase, e.g. comprising an alkylamine, oxoamine) wherein the conjugation occurs exclusively on one or more acceptor glutamine residues present in the targeting moiety outside of the antigen combining site (e.g., outside a variable region, in a constant region). Conjugation thus does not occur on a glutamine, e.g. an at least partly surface exposed glutamine, within the variable region. The FLT3 binding protein, in some examples, is formed by reacting one of the domains with a lysine-based linker in the presence of a TGase.

In some embodiments, where one or more domains within the FLT3 binding proteins are directly joined, a hybrid vector is made where the DNA encoding the directly joined domains are themselves directly ligated to each other. In some embodiments, where linkers are used, a hybrid vector is made where the DNA encoding one domain is ligated to the DNA encoding one end of a linker moiety and the DNA encoding another domain is ligated to the other end of the linker moiety.

In some embodiments, the FLT3 binding protein is a single chain variable fragments (scFv), single-domain antibody such as a heavy chain variable domain (VH), a light chain variable domain (VL) and a variable domain (VHH) of camelid derived single domain antibody. In other embodiments, the FLT3 binding protein is a non-Ig binding domain, i.e., an antibody mimetic, such as anticalins, affilins, affibody molecules, affimers, affitins, alphabodies, avimers, DARPins, fynomers, kunitz domain peptides, and monobodies. In further embodiments, the FLT3 binding protein is a ligand or peptide that binds to or associates with FLT3. In yet further embodiments, the FLT3 binding protein is a knottin. In yet further embodiments, the binding domain to FLT3 is a small molecular entity.

In certain embodiments, the FLT3 binding proteins according to the present disclosure may be incorporated into FLT3 targeting trispecific proteins. In some embodiments, the trispecific proteins comprise a CD3 binding domain, a half-life extension domain, and an FLT3 binding domain according to this disclosure. In some embodiments, the FLT3 binding trispecific protein comprises a trispecific antibody.

Multispecific FLT3 Targeting Proteins, Such as FLT3 Targeting Trispecific Proteins (Also Referred to Herein as FLT3 Targeting TriTAC™ Proteins or Molecules)

In one aspect is described herein a multispecific or a multivalent protein comprising an FLT3 binding protein according to the present disclosure. In some embodiments, the multispecific protein further comprises a domain which specifically binds to a CD3. In some embodiments, the multispecific protein further comprises a domain which specifically binds to human CD3. In some embodiments, the multispecific protein further comprises a domain which specifically binds to CD3-gamma. In some embodiments, the multispecific protein further comprises a domain which specifically binds to CD3-delta. In some embodiments, the multispecific protein further comprises a domain which specifically binds to CD3-epsilon.

In additional embodiments, the multispecific protein further comprises a domain which specifically binds to the T cell receptor (TCR). In some embodiments, the multispecific protein further comprises a domain which specifically binds the alpha chain of the TCR. In some embodiments, the multispecific protein further comprises a domain which specifically binds the beta chain of the TCR.

In certain embodiments, the CD3 binding domain of the multispecific proteins exhibits not only potent CD3 binding affinities with human CD3, but shows excellent cross reactivity with the respective cynomolgus monkey CD3 proteins. In some instances, the CD3 binding domain of the multispecific proteins are cross-reactive with CD3 from cynomolgus monkey. In certain instances, human:cynomolgous KD (hKd: cKd) ratios for CD3 binding are between 20:1 and 1:2.

In some embodiments, the CD3 binding domain of the multispecific protein is any domain that binds to CD3 including but not limited to domains from a monoclonal antibody, a polyclonal antibody, a recombinant antibody, a human antibody, a humanized antibody, or antigen binding fragments of the CD3 binding antibodies, such as single domain antibodies (sdAb), Fab, F(ab′)2, and Fv fragments, fragments comprised of one or more CDRs, single-chain antibodies (e.g., single chain Fv fragments (scFv), disulfide stabilized (dsFv) Fv fragments, heteroconjugate antibodies (e.g., bispecific antibodies), pFv fragments, heavy chain monomers or dimers, light chain monomers or dimers, and dimers consisting of one heavy chain and one light chain. In some instances, it is beneficial for the CD3 binding domain to be derived from the same species in which the multispecific protein comprising a single domain serum albumin binding protein described herein will ultimately be used in. For example, for use in humans, it may be beneficial for the CD3 binding domain of the multispecific protein comprising an FLT3 binding protein described herein to comprise human or humanized residues from the antigen binding domain of an antibody or antibody fragment. Exemplary amino acid sequence for the CD3 binding domain of a multispecific (e.g., trispecific) FLT3 targeting protein of this disclosure is provided as SEQ ID No. 373.

In some embodiments, the serum albumin binding domain (also referred to herein as the half-life extension domain) of a multispecific protein comprising an FLT3 binding protein as described herein can be any domain that binds to serum albumin including but not limited to domains from a monoclonal antibody, a polyclonal antibody, a recombinant antibody, a human antibody, a humanized antibody. In some embodiments, the serum albumin binding domain is a single chain variable fragments (scFv), single-domain antibody such as a heavy chain variable domain (VH), a light chain variable domain (VL) and a variable domain (VHH) of camelid derived sdAb, or antigen binding fragments of the HSA binding antibodies, such as Fab, F(ab′)2, and Fv fragments, fragments comprised of one or more CDRs, single-chain antibodies (e.g., single chain Fv fragments (scFv)), disulfide stabilized (dsFv) Fv fragments, heteroconjugate antibodies (e.g., bispecific antibodies), pFv fragments, heavy chain monomers or dimers, light chain monomers or dimers, and dimers consisting of one heavy chain and one light chain, peptide, ligand or small molecule entity specific for serum albumin. In certain embodiments, the HSA binding domain is a single-domain antibody. In other embodiments, the serum albumin binding domain is a peptide. In further embodiments, the serum albumin binding domain is a small molecule. It is contemplated that the serum albumin binding domain of the multispecific binding protein comprising a single chain variable fragment CD3 binding protein is fairly small and no more than 25 kD, no more than 20 kD, no more than 15 kD, or no more than 10 kD in some embodiments. In certain instances, the serum albumin binding is 5 kD or less if it is a peptide or small molecule entity. Exemplary amino acid sequence for a serum albumin binding domain of a multispecific (e.g., trispecific) FLT3 targeting protein of this disclosure is provided as SEQ ID No. 372.

The half-life extension domain of a multispecific binding protein as described herein, comprising a single chain variable fragment CD3 binding protein provides for altered pharmacodynamics and pharmacokinetics of the single chain variable fragment CD3 binding protein itself. As above, the half-life extension domain extends the elimination half-time. The half-life extension domain also alters pharmacodynamic properties including alteration of tissue distribution, penetration, and diffusion of the single chain variable fragment CD3 binding protein. In some embodiments, the half-life extension domain provides for improved tissue (including tumor) targeting, tissue distribution, tissue penetration, diffusion within the tissue, and enhanced efficacy as compared with a protein without a half-life extension domain. In one embodiment, therapeutic methods effectively and efficiently utilize a reduced amount of the multispecific binding protein comprising a single chain variable fragment CD3 binding protein, resulting in reduced side effects, such as reduced off-target, such as non-tumor cell cytotoxicity.

The half-life extension domain of a multispecific binding protein as described herein, comprising an FLT3 binding domain provides for altered pharmacodynamics and pharmacokinetics of FLT3 binding domain itself. As above, the half-life extension domain extends the elimination half-time. The half-life extension domain also alters pharmacodynamic properties including alteration of tissue distribution, penetration, and diffusion of the FLT3 binding domain. In some embodiments, the half-life extension domain provides for improved tissue (including tumor) targeting, tissue distribution, tissue penetration, diffusion within the tissue, and enhanced efficacy as compared with a protein without a half-life extension domain. In one embodiment, therapeutic methods effectively and efficiently utilize a reduced amount of the multispecific binding protein comprising an FLT3 binding domain, resulting in reduced side effects, such as reduced off-target, such as non-tumor cell cytotoxicity.

Further, the binding affinity of the half-life extension domain, in some embodiments, is selected so as to target a specific elimination half-time in a multispecific binding protein comprising an FLT3 binding protein as described herein. Thus, in some embodiments, the half-life extension domain has a high binding affinity. In other embodiments, the half-life extension domain has a medium binding affinity. In yet other embodiments, the half-life extension domain has a low or marginal binding affinity. Exemplary binding affinities include K_(d) of 10 nM or less (high), between 10 nM and 100 nM (medium), and greater than 100 nM (low). As above, binding affinities to serum albumin are determined by known methods such as Surface Plasmon Resonance (SPR).

An FLT3 targeting multispecific protein of this disclosure, in certain embodiments, comprises (A) a first domain which binds to a CD3; (B) a second domain which is an half-life extension domain; and (C) a third domain which is an FLT3 binding protein as described herein. In certain embodiments, the first domain comprises an scFv that specifically binds the CD3. The CD3 protein comprises, for instance, a human CD3 protein. In certain embodiments, the second domain comprises an sdAb that specifically binds a bulk serum protein. In some instances, the bulk serum protein is albumin, such as, a serum albumin, such as, a human serum albumin.

The domains (A), (B), and (C), are, in some embodiments, linked via linkers L1 and L2, in any one of the following orientations: H₂N-(A)-L1-(C)-L2-(B)-COOH, H₂N-(B)-L1-(A)-L2-(C)-COOH, H₂N-(C)-L1-(B)-L2-(A)-COOH, H₂N-(C)-L1-(A)-L2-(B)-COOH, H₂N-(A)-L1-(B)-(C)-L2-COOH, or H₂N-(B)-(C)-(A)-COOH.

An FLT3 targeting multispecific protein of this disclosure, in some embodiments, comprises an amino acid sequence that is at least about 70% to at least about 100% identical to a sequence selected from the group consisting of SEQ ID Nos. 196-272, and 391-392. In some embodiments, an FLT3 targeting multispecific protein of this disclosure, in some embodiments, comprises an amino acid sequence that is at least about 70%, at least about 75%, at least about 76%, at least about 77%, about 78%, at least about 79%, at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, to at least about 100% identical to a sequence selected from the group consisting of SEQ ID Nos. 196-272, and 391-392.

An FLT3 targeting multispecific protein of this disclosure, in some embodiments, comprises an EC₅₀ of about 0.5 pM to about 6000 pM, such as such as an EC₅₀ from about 0.5 pM to about 1500 pM, about 1 pM to about 4000 pM, about 10 pM to about 2000 pM, about 20 pM to about 1000 pM, about 30 pM to about 40 pM to about 500 pM, or about 50 pM to about 100 pM, in a T cell dependent cellular cytotoxicity (TDCC) assay that measures the potency of the multispecific protein in T cell mediated killing of cells, such as leukemia or lymphoma cells (see, e.g., TDCC EC50 values provided in Table 5 and Table 6). In some embodiments, the EC₅₀ in the TDCC assay is from about 0.5 pM to about 6000 pM, such as from about 0.5 pM to about 35 pM.

Conditionally Active Multispecific FLT3 Targeting Proteins, Such as Conditionally Active FLT3 Targeting Trispecific Proteins (Also Referred to Herein as FLT3 Targeting ProTriTAC™ or Protrispecific Proteins or Molecules)

One embodiment of this disclosure provides a conditionally active multispecific protein comprising an FLT3 binding domain as disclosed herein (for example, in some embodiment this disclosure provides an FLT3 targeting protrispecific/ProTriTAC™ protein comprising an FLT3 binding domain of this disclosure). Examples are illustrated in FIG. 28. In some embodiments, the conditionally active multispecific protein further comprises a domain which specifically binds to a CD3 and a binding moiety which specifically binds to a bulk serum protein, such as a human serum albumin. In some embodiments, the binding moiety is capable of masking the interaction of the FLT3 binding domain or the CD3 binding domain, to their targets. In some embodiments, a binding moiety of this disclosure comprises a masking moiety and a cleavable linker, such as a protease cleavable linker. In some embodiments, the masking moiety comprises a modified non-CDR loop sequence and a non-cleavable linker. The binding moiety is capable of synergistically expanding a therapeutic window of a conditionally active FLT3 targeting protrispecific protein, by both steric masking and specific masking. In some embodiments, the binding moiety combines both steric masking (for example, via binding to a bulk serum albumin) and specific masking (for example, via non-CDR loops binding to the CDRs of an anti-FLT3 domain or an anti-CD3 scFv domain). In some cases, modifying the non-CDR loops within the binding moiety does not affect albumin binding. The protease cleavable linker, in some cases, enables activation of an FLT3 targeting protrispecific protein in a single proteolytic event, thereby allowing more efficient conversion of the protrispecific molecule in tumor microenvironment. Further, tumor-associated proteolytic activation, in some cases, reveals active T cell engager with minimal off-tumor activity after activation. The present disclosure, in some embodiments, provides a half-life extended T cell engager format (ProTriTAC™) comprising an FLT3 binding moiety as described herein, which in some cases represents a new and improved approach to engineer conditionally active T cell engagers.

The half-life of the FLT3 binding domain in a conditionally active protrispecific format is, in some embodiments, extended in systemic circulation by using the binding moiety as described above which acts as a safety switch that keeps the multispecific protein in the pro format in an inert state until it reaches the tumor microenvironment where it is conditionally activated by cleavage of the linker and is able to bind its target antigen(s). The safety switch, in certain instances, provides several advantages: some examples including (i) expanding the therapeutic window of the conditionally active FLT3 targeting protein; (ii) reducing target-mediated drug disposition by maintaining the conditionally active FLT3 targeting protein in systemic circulation; (iii) reducing the concentration of undesirable activated protein in systemic circulation, thereby minimizing the spread of chemistry, manufacturing, and controls related impurities, e.g., pre-activated drug product, endogenous viruses, host-cell proteins, DNA, leachables, anti-foam, antibiotics, toxins, solvents, heavy metals; (iv) reducing the concentration of undesirable activated proteins in systemic circulation, thereby minimizing the spread of product related impurities, aggregates, breakdown products, product variants due to: oxidation, deamidation, denaturation, loss of C-term Lys in MAbs; (v) preventing aberrant activation in circulation; (vi) reducing the toxicities associated with the leakage of activated species from diseased tissue or other pathophysiological conditions, e.g., tumors, autoimmune diseases, inflammations, viral infections, tissue remodeling events (such as myocardial infarction, skin wound healing), or external injury (such as X-ray, CT scan, UV exposure); and (vii) reducing non-specific binding of the conditionally active FLT3 targeting protein. Furthermore, post-activation, or in other words post breaking of the safety switch, the conditionally active FLT3 targeting protein is separated from the safety switch which provided extended half-life, and thus is cleared from circulation.

In some embodiments, the conditionally active FLT3 targeting protein format gives the FLT3 binding domain a significantly longer serum half-life and reduces the likelihood of its undesirable activation in circulation, thereby producing a “biobetter” version.

A binding moiety as described herein comprises at least one non-CDR loop. In some embodiments, a non-CDR loop provides a binding site for binding of the binding moiety to an FLT3 binding domain of this disclosure. In some cases, the binding moiety masks binding of the FLT3 binding domain to its target antigen, e.g., via steric occlusion, via specific intermolecular interactions, or a combination of both.

In some embodiments, a binding moiety as described herein further comprise complementarity determining regions (CDRs), for instance, specific for binding a bulk serum protein (e.g., a human serum albumin). In some instances, a binding moiety of this disclosure is a domain derived from an immunoglobulin molecule (Ig molecule). The Ig may be of any class or subclass (IgG1, IgG2, IgG3, IgG4, IgA, IgE, IgM etc). A polypeptide chain of an Ig molecule folds into a series of parallel beta strands linked by loops. In the variable region, three of the loops constitute the “complementarity determining regions” (CDRs) which determine the antigen binding specificity of the molecule. An IgG molecule comprises at least two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, or an antigen binding fragment thereof. Each heavy chain is comprised of a heavy chain variable region (abbreviated herein as VH) and a heavy chain constant region. The heavy chain constant region is comprised of three domains, CH1, CH2 and CH3. Each light chain is comprised of a light chain variable region (abbreviated herein as VL) and a light chain constant region. The light chain constant region is comprised of one domain, CL. The VH and VL regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDRs) with are hypervariable in sequence and/or involved in antigen recognition and/or usually form structurally defined loops, interspersed with regions that are more conserved, termed framework regions (FR). Each VH and VL is composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. In some embodiments of this disclosure, at least some or all of the amino acid sequences of FR1, FR2, FR3, and FR4 are part of the “non-CDR loop” of the binding moieties described herein. As shown in FIG. 29, a variable domain of an immunoglobulin molecule has several beta strands that are arranged in two sheets. The variable domains of both light and heavy immunoglobulin chains contain three hypervariable loops, or complementarity-determining regions (CDRs). The three CDRs of a V domain (CDR1, CDR2, CDR3) cluster at one end of the beta barrel. The CDRs are the loops that connect beta strands B-C, C′-C″, and F-G of the immunoglobulin fold, whereas the bottom loops that connect beta strands AB, CC′, C″-D and E-F of the immunoglobulin fold, and the top loop that connects the D-E strands of the immunoglobulin fold are the non-CDR loops. In some embodiments of this disclosure, at least some amino acid residues of a constant domain, CH1, CH2, or CH3, are part of the “non-CDR loop” of the binding moieties described herein. Non-CDR loops comprise, in some embodiments, one or more of AB, CD, EF, and DE loops of a C1-set domain of an Ig or an Ig-like molecule; AB, CC′, EF, FG, BC, and EC′ loops of a C2-set domain of an Ig or an Ig-like molecule; DE, BD, GF, A(A1A2)B, and EF loops of I(Intermediate)-set domain of an Ig or Ig-like molecule.

Within the variable domain, the CDRs are believed to be responsible for antigen recognition and binding, while the FR residues are considered a scaffold for the CDRs. However, in certain cases, some of the FR residues play an important role in antigen recognition and binding. Framework region residues that affect Ag binding are divided into two categories. The first are FR residues that contact the antigen, thus are part of the binding-site, and some of these residues are close in sequence to the CDRs. Other residues are those that are far from the CDRs in sequence, but are in close proximity to it in the 3-D structure of the molecule, e.g., a loop in heavy chain.

In some embodiments, the non-CDR loop is modified to generate an antigen binding site specific for a bulk serum protein, such as albumin. It is contemplated that various techniques can be used for modifying the non-CDR loop, e.g., site-directed mutagenesis, random mutagenesis, insertion of at least one amino acid that is foreign to the non-CDR loop amino acid sequence, amino acid substitution. An antigen peptide is inserted into a non-CDR loop, in some examples. In some examples, an antigenic peptide is substituted for the non-CDR loop. The modification, to generate an antigen binding site, is in some cases in only one non-CDR loop. In other instances, more than one non-CDR loop are modified. For instance, the modification is in any one of the non-CDR loops shown in FIG. 29, i.e., AB, CC′, C″ D, EF, and D-E. In some cases, the modification is in the DE loop. In other cases the modifications are in all four of AB, CC′, C″-D, E-F loops. In certain examples, the binding moieties described herein are bound to the FLT3 binding domain via their AB, CC′, C″ D, or EF loop and are bound to a bulk-serum protein, such as albumin, via their B-C, C′-C″, or F-G loop. In certain examples, the binding moiety is bound to the FLT3 binding domain via its AB, CC′, C″ D, and EF loop and is bound to a bulk-serum protein, such as albumin, via its BC, C′C″, and FG loop. In certain examples, the binding moiety is bound to the FLT3 binding domain via one or more of AB, CC′, C″ D, and E-F loop and is bound to a bulk-serum protein, such as albumin, via one or more of BC, C′C″, and FG loop. In certain examples, the binding moiety is bound to a bulk serum protein, such as albumin, via its AB, CC′, C″ D, or EF loop and is bound to the FLT3 binding domain via its BC, C′C″, or FG loop. In certain examples, the binding moiety is bound to a bulk serum protein, such as albumin, via its AB, CC′, C″ D, and EF loop and is bound to the FLT3 binding domain via its BC, C′C″, and FG loop. In certain examples, the binding moiety of the first embodiment is bound to a bulk serum protein, such as albumin, via one or more of AB, CC′, C″ D, and E-F loop and is bound to the FLT3 binding protein, via one or more of BC, C′C″, and FG loop.

The bulk serum protein comprises, for example, albumin, fibrinogen, or a globulin. In some embodiments, the binding moieties are engineered scaffolds. Engineered scaffolds comprise, for example, sdAb, a scFv, a Fab, a VHH, a fibronectin type III domain, immunoglobulin-like scaffold (as suggested in Halaby et al., 1999. Prot Eng 12(7):563-571), DARPin, cystine knot peptide, lipocalin, three-helix bundle scaffold, protein G-related albumin-binding module, or a DNA or RNA aptamer scaffold.

In some cases, the binding moieties comprise a binding site for the bulk serum protein. In some embodiments, the CDRs within the binding moieties provide a binding site for the bulk serum protein. The bulk serum protein is, in some examples, a globulin, albumin, transferrin, IgG1, IgG2, IgG4, IgG3, IgA monomer, Factor XIII, Fibrinogen, IgE, or pentameric IgM. In some embodiments, the binding moieties comprise a binding site for an immunoglobulin light chain. In some embodiments, the CDRs provide a binding site for the immunoglobulin light chain. The immunoglobulin light chain is, in some examples, an Igκ free light chain or an Igλ free light chain.

The binding moieties are any kinds of polypeptides. For example, in certain instances the binding moieties are natural peptides, synthetic peptides, or fibronectin scaffolds, or engineered bulk serum proteins. In some examples, the binding moieties comprise any type of binding domain, including but not limited to, domains from a monoclonal antibody, a polyclonal antibody, a recombinant antibody, a human antibody, a humanized antibody. In some embodiments, the binding moiety is a single chain variable fragment (scFv), a soluble TCR fragment, a single-domain antibody such as a heavy chain variable domain (VH), a light chain variable domain (VL) and a variable domain (VHH) of camelid derived nanobody. In other embodiments, the binding moieties are non-Ig binding domains, i.e., antibody mimetic, such as anticalins, affilins, affibody molecules, affimers, affitins, alphabodies, avimers, DARPins, fynomers, kunitz domain peptides, and monobodies.

Integration into Chimeric Antigen Receptors (CAR)

The FLT3 binding proteins of the present disclosure can, in certain examples, be incorporated into a chimeric antigen receptor (CAR). An engineered immune effector cell, e.g., a T cell or NK cell, can be used to express a CAR that includes an FLT3 binding protein containing, for example, an anti-FLT3 single domain antibody as described herein. In one embodiment, the CAR including the FLT3 binding protein as described herein is connected to a transmembrane domain via a hinge region, and further a costimulatory domain, e.g., a functional signaling domain obtained from OX40, CD27, CD28, CD5, ICAM-1, LFA-1 (CD11a/CD18), ICOS (CD278), or 4-1BB. In some embodiments, the CAR further comprises a sequence encoding an intracellular signaling domain, such as 4-1BB and/or CD3 zeta.

FLT3 Binding Protein Modifications

The FLT3 binding proteins described herein, including FLT3 binding domains (e.g., an FLT3 binding sdAb of this disclosure) and FLT3 targeting multispecific proteins (e.g., an FLT3 targeting trispecific protein as described herein) encompass derivatives or analogs in which (i) an amino acid is substituted with an amino acid residue that is not one encoded by the genetic code, (ii) the mature polypeptide is fused with another compound such as polyethylene glycol, or (iii) additional amino acids are fused to the protein, such as a leader or secretory sequence or a sequence for purification of the protein.

Typical modifications include, but are not limited to, acetylation, acylation, ADP-ribosylation, amidation, covalent attachment of flavin, covalent attachment of a heme moiety, covalent attachment of a nucleotide or nucleotide derivative, covalent attachment of a lipid or lipid derivative, covalent attachment of phosphatidylinositol, cross-linking, cyclization, disulfide bond formation, demethylation, formation of covalent crosslinks, formation of cystine, formation of pyroglutamate, formylation, gamma carboxylation, glycosylation, GPI anchor formation, hydroxylation, iodination, methylation, myristoylation, oxidation, proteolytic processing, phosphorylation, prenylation, racemization, selenoylation, sulfation, transfer-RNA mediated addition of amino acids to proteins such as arginylation, and ubiquitination.

Modifications are made anywhere in the FLT3 binding proteins described herein, including the peptide backbone, the amino acid side-chains, and the amino or carboxyl termini. Certain common peptide modifications that are useful for modification of the FLT3 binding proteins include glycosylation, lipid attachment, sulfation, gamma-carboxylation of glutamic acid residues, hydroxylation, blockage of the amino or carboxyl group in a polypeptide, or both, by a covalent modification, and ADP-ribosylation.

In some embodiments, derivatives of the FLT3 binding proteins as described herein comprise immunoreactive modulator derivatives and antigen binding molecules comprising one or more modifications.

In some embodiments, the FLT3 binding proteins of the disclosure are monovalent or multivalent bivalent, trivalent, etc.). As used herein, the term “valency” refers to the number of potential target binding sites associated with an antibody. Each target binding site specifically binds one target molecule or specific position or locus on a target molecule. When an antibody is monovalent, each binding site of the molecule will specifically bind to a single antigen position or epitope. When an antibody comprises more than one target binding site (multivalent), each target binding site may specifically bind the same or different molecules (e.g., may bind to different ligands or different antigens, or different epitopes or positions on the same antigen).

In some embodiments, the FLT3 binding proteins as set forth above are fused to an Fc region from any species, including but not limited to, human immunoglobulin, such as human IgG1, a human IgG2, a human IgG3, human IgG4, to generate Fc-fusion FLT3 binding proteins. In some embodiments, the Fc-fusion FLT3 binding proteins of this disclosure have extended half-life compared to an otherwise identical FLT3 binding protein. In some embodiments, the Fc-fusion FLT3 binding proteins of this disclosure contain inter alia one or more additional amino acid residue substitutions, mutations and/or modifications, e.g., in the Fc region. which result in a binding protein with preferred characteristics including, but not limited to: altered pharmacokinetics, extended serum half-life.

In some embodiments, such Fc-fused FLT3 binding proteins provide extended half-lives in a mammal, such as in a human, of greater than 5 days, greater than 10 days, greater than 15 days, greater than 20 days, greater than 25 days, greater than 30 days, greater than 35 days, greater than 40 days, greater than 45 days, greater than 2 months, greater than 3 months, greater than 4 months, or greater than 5 months. The increased half-life, in some cases, results in a higher serum titer which thus reduces the frequency of the administration of the FLT3 binding proteins and/or reduces the concentration of the antibodies to be administered. Binding to human FcRn in vivo and serum half-life of human FcRn high affinity binding polypeptides is assayed, in some examples, in transgenic mice or transfected human cell lines expressing human FcRn, or in primates to which the polypeptides with a variant Fc region are administered.

The FLT3 binding proteins, in some cases, are differentially modified during or after production, e.g., by glycosylation, acetylation, phosphorylation, amidation, derivatization by known protecting/blocking groups, proteolytic cleavage, linkage to an antibody molecule or other cellular ligand, etc. Any of numerous chemical modifications are carried out by techniques, including but not limited, to specific chemical cleavage by cyanogen bromide, trypsin, chymotrypsin, papain, V8 protease, NaBH4, acetylation, formylation, oxidation, reduction, metabolic synthesis in the presence of tunicamycin, etc.

Various post-translational modifications of the FLT3 binding proteins also encompassed by the disclosure include, for example, N-linked or O-linked carbohydrate chains, processing of N-terminal or C-terminal ends, attachment of chemical moieties to the amino acid backbone, chemical modifications of N-linked or O-linked carbohydrate chains, and addition or deletion of an N-terminal methionine residue as a result of prokaryotic host cell expression. Moreover, the FLT3 binding proteins are, in some cases, modified with a detectable label, such as an enzymatic, fluorescent, radioisotopic or affinity label to allow for detection and isolation of the modulator.

Polynucleotides Encoding FLT3 Binding Proteins

Also provided, in some embodiments, are polynucleotide molecules encoding FLT3 binding proteins described herein. In some embodiments, the polynucleotide molecules are provided as a DNA construct. In other embodiments, the polynucleotide molecules are provided as a messenger RNA transcript.

The polynucleotide molecules are constructed by known methods such as by combining the genes encoding a single domain FLT3 binding protein or gene encoding various domains of FLT3 binding proteins comprising more than one domain. In some embodiments, the gene encoding the domains are either separated by peptide linkers or, in other embodiments, directly linked by a peptide bond, into a single genetic construct operably linked to a suitable promoter, and optionally a suitable transcription terminator, and expressing it in bacteria or other appropriate expression system such as, for example CHO cells. Depending on the vector system and host utilized, any number of suitable transcription and translation elements, including constitutive and inducible promoters, may be used. The promoter is selected such that it drives the expression of the polynucleotide in the respective host cell.

In some embodiments, the polynucleotide coding for an FLT3 binding protein as described herein is inserted into a vector, preferably an expression vector, which represents a further embodiment. This recombinant vector can be constructed according to known methods. Vectors of particular interest include plasmids, phagemids, phage derivatives, virii (e.g., retroviruses, adenoviruses, adeno-associated viruses, herpes viruses, lentiviruses, and the like), and cosmids.

A variety of expression vector/host systems may be utilized to contain and express the polynucleotide encoding the polypeptide of the described FLT3 binding protein. Examples of expression vectors for expression in E. coli are pSKK (Le Gall et al., J Immunol Methods. (2004) 285(1):111-27) or pcDNA5 (Invitrogen) for expression in mammalian cells.

Thus, the FLT3 binding proteins as described herein, in some embodiments, are produced by introducing a vector encoding the protein as described above into a host cell and culturing said host cell under conditions whereby the protein domains are expressed, may be isolated and, optionally, further purified.

Pharmaceutical Compositions

Also provided, in some embodiments, are pharmaceutical compositions comprising an anti-FLT3 binding protein described herein, a vector comprising the polynucleotide encoding the polypeptide of the FLT3 binding proteins or a host cell transformed by this vector and at least one pharmaceutically acceptable carrier. The term “pharmaceutically acceptable carrier” includes, but is not limited to, any carrier that does not interfere with the effectiveness of the biological activity of the ingredients and that is not toxic to the patient to whom it is administered. Examples of suitable pharmaceutical carriers are well known in the art and include phosphate buffered saline solutions, water, emulsions, such as oil/water emulsions, various types of wetting agents, sterile solutions etc. Such carriers can be formulated by conventional methods and can be administered to the subject at a suitable dose. Preferably, the compositions are sterile. These compositions may also contain adjuvants such as preservative, emulsifying agents and dispersing agents. Prevention of the action of microorganisms may be ensured by the inclusion of various antibacterial and antifungal agents. A further embodiment provides one or more of the above described FLT3 binding proteins packaged in lyophilized form, or packaged in an aqueous medium.

In some embodiments of the pharmaceutical compositions, the FLT3 binding proteins described herein are encapsulated in nanoparticles. In some embodiments, the nanoparticles are fullerenes, liquid crystals, liposome, quantum dots, superparamagnetic nanoparticles, dendrimers, or nanorods. In other embodiments of the pharmaceutical compositions, the FLT3 binding protein is attached to liposomes. In some instances, the FLT3 binding proteins are conjugated to the surface of liposomes. In some instances, the FLT3 binding proteins are encapsulated within the shell of a liposome. In some instances, the liposome is a cationic liposome.

The FLT3 binding proteins described herein are contemplated for use as a medicament. Administration is effected by different ways, e.g. by intravenous, intraperitoneal, subcutaneous, intramuscular, topical or intradermal administration. In some embodiments, the route of administration depends on the kind of therapy and the kind of compound contained in the pharmaceutical composition. The dosage regimen will be determined by the attending physician and other clinical factors. Dosages for any one patient depends on many factors, including the patient's size, body surface area, age, sex, the particular compound to be administered, time and route of administration, the kind of therapy, general health and other drugs being administered concurrently. An “effective dose” refers to amounts of the active ingredient that are sufficient to affect the course and the severity of the disease, leading to the reduction or remission of such pathology and may be determined using known methods.

In some embodiments, the FLT3 binding proteins of this disclosure are administered at a dosage of up to 10 mg/kg at a frequency of once a week. In some cases, the dosage ranges from about 1 ng/kg to about 10 mg/kg, for example about 1 ng/kg to about 70 ng/kg, about 1 ng/kg to about 160 ng/kg, about 1 ng/kg to about 200 ng/kg. In some embodiments, the dose is from about 1 ng/kg to about 10 ng/kg, about 5 ng/kg to about 15 ng/kg, about 12 ng/kg to about 20 ng/kg, about 18 ng/kg to about 30 ng/kg, about 25 ng/kg to about 50 ng/kg, about 35 ng/kg to about 60 ng/kg, about 45 ng/kg to about 70 ng/kg, about 65 ng/kg to about 85 ng/kg, about 80 ng/kg to about 1 μg/kg, about 0.5 μg/kg to about 5 μg/kg, about 2 μg/kg to about 10 μg/kg, about 7 μg/kg to about 15 μg/kg, about 12 μg/kg to about 25 μg/kg, about 20 μg/kg to about 50 μg/kg, about 35 μg/kg to about 70 μg/kg, about 45 μg/kg to about 80 μg/kg, about 65 μg/kg to about 90 μg/kg, about 85 μg/kg to about 0.1 mg/kg, about 0.095 mg/kg to about 10 mg/kg. In some cases, the dosage is about 0.1 mg/kg to about 0.2 mg/kg; about 0.25 mg/kg to about 0.5 mg/kg, about 0.45 mg/kg to about 1 mg/kg, about 0.75 mg/kg to about 3 mg/kg, about 2.5 mg/kg to about 4 mg/kg, about 3.5 mg/kg to about 5 mg/kg, about 4.5 mg/kg to about 6 mg/kg, about 5.5 mg/kg to about 7 mg/kg, about 6.5 mg/kg to about 8 mg/kg, about 7.5 mg/kg to about 9 mg/kg, or about 8.5 mg/kg to about 10 mg/kg. The frequency of administration, in some embodiments, is about less than daily, every other day, less than once a day, twice a week, weekly, once in 7 days, once in two weeks, once in three weeks, once in four weeks, or once a month. In some cases, the frequency of administration is weekly. In some cases, the frequency of administration is weekly and the dosage is up to 10 mg/kg. In some cases, duration of administration is from about 1 day to about 4 weeks or longer.

Methods of Treatment

Also provided in certain embodiments are methods of treating a condition associated with malignant cells expressing FLT3 in a subject comprising administering to a subject in need thereof an effective amount of an FLT3 binding domains or multispecific proteins (including conditionally active multispecific proteins) comprising an FLT3 binding domain of this disclosure, or a CAR comprising an FLT3 binding protein as described herein, or a pharmaceutical composition comprising the same. In some embodiments, the condition is a cancer. In some embodiment the condition is a hematologic malignancy derived from either of the two major blood cell lineages, i.e., the myeloid cell line (which produces granulocytes, erythrocytes, thrombocytes, macrophages and mast cells) or lymphoid cell line (which produces B, T, NK and plasma cells), such as all types of leukemias, lymphomas, and myelomas, e.g., acute, chronic, lymphocytic and/or myelogenous leukemias, such as acute leukemia (ALL), acute myelogenous leukemia (AML), myeloid leukemia, chronic lymphocytic leukemia (CLL), and chronic myelogenous leukemia (CIVIL), chronic myelomonocytic leukemia, undifferentiated AML (MO), myeloblastic leukemia (M1), myeloblastic leukemia (M2; with cell maturation), promyelocytic leukemia (M3 or M3 variant [M3V]), myelomonocytic leukemia (M4 or M4 variant with eosinophilia [M4E]), monocytic leukemia (M5), erythroleukemia (M6), megakaryoblastic leukemia (M7), isolated granulocytic sarcoma, and chloroma; lymphomas, such as Hodgkin's lymphoma (HL), non-Hodgkin's lymphoma (NEIL), B-cell lymphomas, T-cell lymphomas, lymphoplasmacytoid lymphoma, monocytoid B-cell lymphoma, mucosa-associated lymphoid tissue (MALT) lymphoma, anaplastic (e.g., Ki 1+) large-cell lymphoma, adult T-cell lymphoma/leukemia, mantle cell lymphoma, angio immunoblastic T-cell lymphoma, angiocentric lymphoma, intestinal T-cell lymphoma, primary mediastinal B-cell lymphoma, precursor T-lymphoblastic lymphoma, T-lymphoblastic; and lymphoma/leukemia (T-Lbly/T-ALL), peripheral T-cell lymphoma, lymphoblastic lymphoma, post-transplantation lymphoproliferative disorder, true histiocytic lymphoma, primary central nervous system lymphoma, primary effusion lymphoma, lymphoblastic lymphoma (LBL), hematopoietic tumors of lymphoid lineage, acute lymphoblastic leukemia, diffuse large B-cell lymphoma, Burkitt's lymphoma, marginal zone lymphoma, nodal marginal zone B cell lymphoma, splenic marginal zone lymphoma, follicular lymphoma, diffuse histiocytic lymphoma (DHL), mucosa-associated lymphatic tissue lymphoma, small cell lymphocytic lymphoma, immunoblastic large cell lymphoma, precursor B-lymphoblastic lymphoma, cutaneous T-cell lymphoma (CTLC) (also called mycosis fungoides or Sezary syndrome), intravascular large B-cell lymphoma, lymphomatoid granulomatosis, T cell/histiocyte-rich large B-cell lymphoma, primary cutaneous diffuse large B-cell lymphoma (leg type), EBV positive diffuse large B-cell lymphoma of the elderly, diffuse large B-cell lymphoma associated with inflammation, intravascular large B-cell lymphoma, ALK-positive large B-cell lymphoma, plasmablastic lymphoma, large B-cell lymphoma arising in HHV8-associated multicentric Castleman disease, B-cell lymphoma unclassified with features intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma, B-cell lymphoma unclassified with features intermediate between diffuse large B-cell lymphoma and classical Hodgkin lymphomalymphoplasmactyic lymphoma, and lymphoplasmacytoid lymphoma (LPL) with Waldenstrom's macroglobulinemia; myelomas, such as IgG myeloma, light chain myeloma, nonsecretory myeloma, smoldering myeloma (also called indolent myeloma), solitary plasmocytoma, and multiple myelomas, chronic lymphocytic leukemia (CLL), hairy cell lymphoma; hematopoietic tumors of myeloid lineage, tumors of mesenchymal origin, including fibrosarcoma and rhabdomyoscarcoma; seminoma, teratocarcinoma, tumors of the central and peripheral nervous, including astrocytoma, schwannomas; tumors of mesenchymal origin, including fibrosarcoma, rhabdomyoscaroma, and osteosarcoma; and other tumors, including melanoma, xeroderma pigmentosum, keratoacanthoma, seminoma, thyroid follicular cancer and teratocarcinoma, hematopoietic tumors of lymphoid lineage, for example T-cell and B-cell tumors, including but not limited to T-cell disorders such as T-prolymphocytic leukemia (T-PLL), including of the small cell and cerebriform cell type; large granular lymphocyte leukemia (LGL) preferably of the T-cell type; a/d T-NHL hepatosplenic lymphoma; peripheral/post-thymic T cell lymphoma (pleomorphic and immunoblastic subtypes); angiocentric (nasal) T-cell lymphoma; cancer of the head or neck, renal cancer, rectal cancer, cancer of the thyroid gland; acute myeloid lymphoma, as well as any combinations of said cancers.

In some embodiments, the condition is Myelodysplastic syndrome (“MDS”) which refers to a diverse group of hematopoietic stem cell disorders. MDS is characterized by a cellular marrow with impaired morphology and maturation (dysmyelopoiesis), peripheral blood cytopenias, and a variable risk of progression to acute leukemia, resulting from ineffective blood cell production.

In another aspect, the disclosure provides a method of inhibiting tumor growth or progression in a subject who has malignant cells expressing FLT3, comprising administering to the subject in need thereof an effective amount of an FLT3 binding domains or multispecific proteins comprising an FLT3 binding domain of this disclosure, or a CAR comprising an FLT3 binding protein as described herein, or a pharmaceutical composition comprising the same. In another aspect, the disclosure provides a method of inhibiting metastasis of malignant cells expressing FLT3 in a subject, comprising administering to the subject in need thereof an effective amount of an FLT3 binding domains or multispecific proteins comprising an FLT3 binding domain of this disclosure, or a pharmaceutical composition comprising the same. In another aspect, the disclosure provides a method of inducing tumor regression in a subject who has malignant cells expressing FLT3, comprising administering to the subject in need thereof an effective amount of an FLT3 binding domains or multi specific proteins comprising an FLT3 binding domain of this disclosure, or a pharmaceutical composition comprising the same. In some embodiments, the methods as described herein further comprise administering an effective amount of a second therapeutic agent. In some embodiments, the second therapeutic agent is a biotherapeutic agent, for example, an antibody. In some embodiments, the second therapeutic agent is a cytokine, TNFa (Tumor Necrosis Factor alpha), a PAP (phosphatidic acid phosphatase) inhibitor, an oncolytic virus, a kinase inhibitor, an IDO (Indoleamine-pyrrole 2,3-dioxygenase) inhibitor, a glutaminase GLS1 inhibitor, a CAR (Chimeric Antigen Receptor)-T cell or T cell therapy, a TLR (Toll-Like Receptor) Agonist (e.g., TLR3, TLR4, TLR5, TLR7, TLR9), or a tumor vaccine.

In some embodiments, the FLT3 binding protein of this disclosure or a pharmaceutical composition comprising the same, reduces the growth of tumor cells in vivo when administered to a subject who has tumor cells that express FLT3. Measurement of the reduction of the growth of tumor cells can be determined by multiple different methodologies well known in the art. Nonlimiting examples include direct measurement of tumor dimension, measurement of excised tumor mass and comparison to control subjects, measurement via imaging techniques (e.g., CT or Mill) that may or may not use isotopes or luminescent molecules (e.g., luciferase) for enhanced analysis, and the like. In specific embodiments, administration of the FLT3 binding proteins of the disclosure or a pharmaceutical composition comprising the same results in a reduction of in vivo growth of tumor cells as compared to a control antigen binding agent by at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%, with an about 100% reduction in tumor growth indicating a complete response and disappearance of the tumor. In further embodiments, administration of the FLT3 binding proteins of the disclosure or a pharmaceutical composition comprising the same results in a reduction of in vivo growth of tumor cells as compared to a control antigen binding agent by about 50-100%, about 75-100% or about 90-100%. In further embodiments, administration of the FLT3 binding proteins of the disclosure or a pharmaceutical composition comprising the same results in a reduction of in vivo growth of tumor cells as compared to a control antigen binding agent by about 50-60%, about 60-70%, about 70-80%, about 80-90%, or about 90-100%.

In some embodiments, the FLT3 binding proteins of the present disclosure are administered to treat a neoplastic condition. Neoplastic conditions, in some embodiments, are benign or malignant; solid tumors or other blood neoplasia; and, in some embodiments, are selected from the group including, but not limited to: adrenal gland tumors, AIDS-associated cancers, alveolar soft part sarcoma, astrocytic tumors, autonomic ganglia tumors, bladder cancer (squamous cell carcinoma and transitional cell carcinoma), blastocoelic disorders, bone cancer (adamantinoma, aneurismal bone cysts, osteochondroma, osteosarcoma), brain and spinal cord cancers, metastatic brain tumors, breast cancer including triple negative breast cancer, carotid body tumors, cervical cancer, chondrosarcoma, chordoma, chromophobe renal cell carcinoma, clear cell carcinoma, colon cancer, colorectal cancer, cutaneous benign fibrous histiocytomas, desmoplastic small round cell tumors, ependymomas, epithelial disorders, Ewing's tumors, extraskeletal myxoid chondrosarcoma, fibrogenesis imperfecta ossium, fibrous dysplasia of the bone, gallbladder and bile duct cancers, gastric cancer, gastrointestinal, gestational trophoblastic disease, germ cell tumors, glandular disorders, head and neck cancers, hypothalamic, intestinal cancer, islet cell tumors, Kaposi's Sarcoma, kidney cancer (nephroblastoma, papillary renal cell carcinoma), leukemias, lipoma/benign lipomatous tumors, liposarcoma/malignant lipomatous tumors, liver cancer (hepatoblastoma, hepatocellular carcinoma), lymphomas, lung cancers (small cell carcinoma, adenocarcinoma, squamous cell carcinoma, large cell carcinoma etc.), macrophagal disorders, medulloblastoma, melanoma, meningiomas, multiple endocrine neoplasia, multiple myeloma, myelodysplastic syndrome, neuroblastoma, neuroendocrine tumors, ovarian cancer, pancreatic cancers, papillary thyroid carcinomas, parathyroid tumors, pediatric cancers, peripheral nerve sheath tumors, phaeochromocytoma, pituitary tumors, prostate cancer, posterior unveal melanoma, rare hematologic disorders, renal metastatic cancer, rhabdoid tumor, rhabdomyosarcoma, sarcomas, skin cancer, soft-tissue sarcomas, squamous cell cancer, stomach cancer, stromal disorders, synovial sarcoma, testicular cancer, thymic carcinoma, thymoma, thyroid metastatic cancer, and uterine cancers (carcinoma of the cervix, endometrial carcinoma, and leiomyoma).

In certain embodiments the FLT3 binding proteins of the present disclosure are used as a front line therapy and administered to subjects who have not previously been treated for the cancerous condition. In other embodiments the FLT3 binding proteins of the present disclosure are used to treat subjects that have previously been treated (with an FLT3 binding protein of this disclosure or with other anti-cancer agent) and have relapsed or determined to be refractory to the previous treatment. In some embodiments the FLT3 binding proteins of the present disclosure are used to treat subjects that have recurrent tumors. In some aspects, the FLT3 binding proteins of the present disclosure are administered to treat a proliferative disorder comprising a solid tumor including, but not limited to, adrenal, liver, kidney, bladder, breast, gastric, ovarian, cervical, uterine, esophageal, colorectal, prostate, pancreatic, lung (both small cell and non-small cell), thyroid, carcinomas, sarcomas, glioblastomas and various head and neck tumors. In some embodiments, the FLT3 binding proteins of the present disclosure are administered to a subject suffering from melanoma. In some embodiments, the FLT3 binding proteins of the present disclosure are used to diagnose, monitor, treat or prevent melanoma. The term “melanoma,” as used herein, includes all types of melanoma including, but not limited to, primary melanoma, malignant melanoma, cutaneous melanoma, extracutaneous melanoma, superficial spreading melanoma, polypoid melanoma, melanocarcinomas, melano epitheliomas, melano sarcomas, melanoma in situ, nodular malignant melanoma, lentigo maligna melanoma, lentiginous melanoma, lentiginous malignant melanoma, mucosal lentiginous melanoma, mucosal melanoma, acral lentiginous melanoma, soft tissue melanoma, ocular melanoma, invasive melanoma, familial atypical mole and melanoma (FAM-M) syndrome, desmoplastic malignant melanoma or uveal melanoma. In some embodiments, possible indications for administration of the FLT3 binding proteins of this disclosure or pharmaceutical compositions comprising the same are tumorous diseases especially epithelial cancers/carcinomas such as breast cancer, colon cancer, prostate cancer, head and neck cancer, skin cancer, cancers of the genito-urinary tract, e.g., ovarian cancer, endometrial cancer, cervix cancer and kidney cancer, lung cancer, gastric cancer, cancer of the small intestine, liver cancer, pancreas cancer, gall bladder cancer, cancers of the bile duct, esophagus cancer, cancer of the salivatory glands and cancer of the thyroid gland. In some embodiments, the administration of the FLT3 binding proteins of this disclosure or pharmaceutical compositions comprising the same is indicated for minimal residual disease, such as early solid tumor, advanced solid tumor or metastatic solid tumor, which is characterized by the local and non-local reoccurrence of the tumor caused by the survival of single cells.

In selected aspects an FLT3 binding proteins of the disclosure is incorporated into a chimeric antigen receptors (CAR) and the FLT3 CAR is administered in a CAR based therapy effective at treating a cancer, such as: a hematologic malignancy derived from either of the two major blood cell lineages, i.e., the myeloid cell line (which produces granulocytes, erythrocytes, thrombocytes, macrophages and mast cells) or lymphoid cell line (which produces B, T, NK and plasma cells), such as all types of leukemias, lymphomas, and myelomas, e.g., AML; epithelial cancers/carcinomas such as breast cancer; colon cancer, prostate cancer; head and neck cancer; skin cancer; cancers of the genito-urinary tract, e.g., ovarian cancer, endometrial cancer, cervix cancer and kidney cancer; lung cancer; gastric cancer; cancer of the small intestine; liver cancer; pancreas cancer; gall bladder cancer; cancers of the bile duct; esophagus cancer; cancer of the salivatory glands and cancer of the thyroid gland; small cell lung cancer; non-small cell lung cancer (e.g., squamous cell non-small cell lung cancer or squamous cell small cell lung cancer) and large cell neuroendocrine carcinoma (LCNEC).

A chimeric antigen receptor is generally an artificially constructed hybrid protein or polypeptide containing or comprising an antigen binding domain of an antibody linked to a signaling domain (e.g., T-cell signaling or T-cell activation domains). In some embodiments, CARs comprising the FLT3 binding proteins of the present disclosure have the ability to redirect the specificity and reactivity of sensitized lymphocytes (e.g., T-cells) toward FLT3 positive target cells in a non-WIC-restricted manner by exploiting the antigen-binding properties of antibodies or antigen binding fragments thereof. The non-WIC-restricted antigen recognition gives T-cells expressing FLT3 CARs the ability to recognize tumorigenic FLT3 independent of antigen processing, thus bypassing a major mechanism of tumor escape. Moreover, when expressed in T-cells, CARs advantageously do not dimerize with endogenous T cell receptor (TCR) alpha and beta chains. In some embodiments the disclosed FLT3 binding proteins are administered to refractory patients (i.e., those whose disease recurs during or shortly after completing a course of initial therapy); sensitive patients (i.e., those whose relapse is longer than 2-3 months after primary therapy); or patients exhibiting resistance to a platinum based agent (e.g., carboplatin, cisplatin, oxaliplatin) and/or a taxane (e.g., docetaxel, paclitaxel, larotaxel or cabazitaxel). In another embodiment the disclosed FLT3 CAR treatments are effective at treating ovarian cancer, including ovarian-serous carcinoma and ovarian-papillary serous carcinoma.

In another embodiment the FLT3 binding proteins of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof are used in maintenance therapy to reduce or eliminate the chance of tumor recurrence following the initial presentation of the disease. In some cases, the disorder has been treated and the initial tumor mass eliminated, reduced or otherwise ameliorated so the patient is asymptomatic or in remission. At such time the subject is administered pharmaceutically effective amounts of the disclosed the FLT3 binding proteins of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof one or more times regardless of if there is little or no indication of disease using standard diagnostic procedures. In some embodiments, the FLT3 binding proteins of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof is administered on a regular schedule over a period of time, such as weekly, every two weeks, monthly, every six weeks, every two months, every three months every six months or annually, for example, to reduce the potential of disease recurrence. Moreover such treatments are in some embodiments continued for a period of weeks, months, years or even indefinitely depending on the patient response and clinical and diagnostic parameters.

In yet another embodiment, the FLT3 binding proteins of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof are used to prophylactically or as an adjuvant therapy to prevent or reduce the possibility of tumor metastasis following a debulking procedure. As used in the present disclosure a “debulking procedure,” is means any procedure, technique or method that eliminates, reduces, treats or ameliorates a tumor or tumor proliferation. Exemplary debulking procedures include, but are not limited to, surgery, radiation treatments (i.e., beam radiation), chemotherapy, immunotherapy or ablation. In some embodiments, at appropriate times, the FLT3 binding proteins of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof are administered as suggested by clinical, diagnostic or theranostic procedures to reduce tumor metastasis. In some embodiments, the dosing regimen is accompanied by appropriate diagnostic or monitoring techniques that allow it to be modified.

Yet other embodiments of the disclosure comprise administering the FLT3 binding protein of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof to subjects that are asymptomatic but at risk of developing a proliferative disorder. That is, in some embodiments, the FLT3 binding protein of the disclosure, the FLT3 CAR, or the FLT3 sensitized lymphocytes, or any combination thereof are used in preventative sense and given to patients that have been examined or tested and have one or more noted risk factors (e.g., genomic indications, family history, in vivo or in vitro test results, etc.) but have not developed neoplasia. In such cases those skilled in the art would be able to determine an effective dosing regimen through empirical observation or through accepted clinical practices.

In some embodiments of the methods described herein, the FLT3 binding proteins, or compositions as described herein are administered in combination with an agent for treatment of the particular disease, disorder or condition. Agents include but are not limited to, therapies involving antibodies, small molecules (e.g., chemotherapeutics), hormones (steroidal, peptide, and the like), radiotherapies (γ-rays, X-rays, and/or the directed delivery of radioisotopes, microwaves, UV radiation and the like), gene therapies (e.g., antisense, retroviral therapy and the like) and other immunotherapies. In some embodiments, an FLT3 binding protein as described herein is administered in combination with anti-diarrheal agents, anti-emetic agents, analgesics, opioids and/or non-steroidal anti-inflammatory agents. In some embodiments, an FLT3 binding protein as described herein is administered in combination with anti-cancer agents. Nonlimiting examples of anti-cancer agents that can be used in the various embodiments of the disclosure, including pharmaceutical compositions and dosage forms and kits of the disclosure, include: acivicin; aclarubicin; acodazole hydrochloride; acronine; adozelesin; aldesleukin; altretamine; ambomycin; ametantrone acetate; aminoglutethimide; amsacrine; anastrozole; anthramycin; asparaginase; asperlin; azacitidine; azetepa; azotomycin; batimastat; benzodepa; bicalutamide; bisantrene hydrochloride; bisnafide dimesylate; bizelesin; bleomycin sulfate; brequinar sodium; bropirimine; busulfan; cactinomycin; calusterone; caracemide; carbetimer; carboplatin; carmustine; carubicin hydrochloride; carzelesin; cedefingol; chlorambucil; cirolemycin; cisplatin; cladribine; crisnatol mesylate; cyclophosphamide; cytarabine; dacarbazine; dactinomycin; daunorubicin hydrochloride; decitabine; dexormaplatin; dezaguanine; dezaguanine mesylate; diaziquone; docetaxel; doxorubicin; doxorubicin hydrochloride; droloxifene; droloxifene citrate; dromostanolone propionate; duazomycin; edatrexate; eflornithine hydrochloride; elsamitrucin; enloplatin; enpromate; epipropidine; epirubicin hydrochloride; erbulozole; esorubicin hydrochloride; estramustine; estramustine phosphate sodium; etanidazole; etoposide; etoposide phosphate; etoprine; fadrozole hydrochloride; fazarabine; fenretinide; floxuridine; fludarabine phosphate; fluorouracil; flurocitabine; fosquidone; fostriecin sodium; gemcitabine; gemcitabine hydrochloride; hydroxyurea; idarubicin hydrochloride; ifosfamide; ilmofosine; interleukin II (including recombinant interleukin II, or rIL2), interferon alpha-2a; interferon alpha-2b; interferon alpha-n1 interferon alpha-n3; interferon beta-I a; interferon gamma-I b; iproplatin; irinotecan hydrochloride; lanreotide acetate; letrozole; leuprolide acetate; liarozole hydrochloride; lometrexol sodium; lomustine; losoxantrone hydrochloride; masoprocol; maytansine; mechlorethamine hydrochloride; megestrol acetate; melengestrol acetate; melphalan; menogaril; mercaptopurine; methotrexate; methotrexate sodium; metoprine; meturedepa; mitindomide; mitocarcin; mitocromin; mitogillin; mitomalcin; mitomycin; mitosper; mitotane; mitoxantrone hydrochloride; mycophenolic acid; nocodazole; nogalamycin; ormaplatin; oxisuran; paclitaxel; pegaspargase; peliomycin; pentamustine; peplomycin sulfate; perfosfamide; pipobroman; piposulfan; piroxantrone hydrochloride; plicamycin; plomestane; porfimer sodium; porfiromycin; prednimustine; procarbazine hydrochloride; puromycin; puromycin hydrochloride; pyrazofurin; riboprine; rogletimide; safingol; safingol hydrochloride; semustine; simtrazene; sparfosate sodium; sparsomycin; spirogermanium hydrochloride; spiromustine; spiroplatin; streptonigrin; streptozocin; sulofenur; talisomycin; tecogalan sodium; tegafur; teloxantrone hydrochloride; temoporfin; teniposide; teroxirone; testolactone; thiamiprine; thioguanine; thiotepa; tiazofurin; tirapazamine; toremifene citrate; trestolone acetate; triciribine phosphate; trimetrexate; trimetrexate glucuronate; triptorelin; tubulozole hydrochloride; uracil mustard; uredepa; vapreotide; verteporfin; vinblastine sulfate; vincristine sulfate; vindesine; vindesine sulfate; vinepidine sulfate; vinglycinate sulfate; vinleurosine sulfate; vinorelbine tartrate; vinzolidine sulfate; vinzolidine sulfate; vorozole; zeniplatin; zinostatin; zorubicin hydrochloride. Other examples of anti-cancer drugs include, but are not limited to: 20-epi-1,25 dihydroxyvitamin D3; 5-ethynyluracil; abiraterone; aclarubicin; acylfulvene; adecypenol; adozelesin; aldesleukin; ALL-TK antagonists; altretamine; ambamustine; amidox; amifostine; aminolevulinic acid; amrubicin; amsacrine; anagrelide; anastrozole; andrographolide; angiogenesis inhibitors; antagonist D; antagonist G; antarelix; anti-dorsalizing morphogenetic protein-1; antiandrogen, prostatic carcinoma; antiestrogen; antineoplaston; antisense oligonucleotides; aphidicolin glycinate; apoptosis gene modulators; apoptosis regulators; apurinic acid; ara-CDP-DL-PTBA; arginine deaminase; asulacrine; atamestane; atrimustine; axinastatin 1; axinastatin 2; axinastatin 3; azasetron; azatoxin; azatyrosine; baccatin III derivatives; balanol; batimastat; BCR/ABL antagonists; benzochlorins; benzoylstaurosporine; beta lactam derivatives; beta-alethine; betaclamycin B; betulinic acid; bFGF inhibitor; bicalutamide; bisantrene; bisaziridinylspermine; bisnafide; bistratene A; bizelesin; breflate; bropirimine; budotitane; buthionine sulfoximine; calcipotriol; calphostin C; camptothecin derivatives; canarypox IL-2; capecitabine; carboxamide-amino-triazole; carboxyamidotriazole; CaRest M3; CARN 700; cartilage derived inhibitor; carzelesin; casein kinase inhibitors (ICOS); castanospermine; cecropin B; cetrorelix; chlorins; chloroquinoxaline sulfonamide; cicaprost; cis-porphyrin; cladribine; clomifene analogues; clotrimazole; collismycin A; collismycin B; combretastatin A4; combretastatin analogue; conagenin; crambescidin 816; crisnatol; cryptophycin 8; cryptophycin A derivatives; curacin A; cyclopentanthraquinones; cycloplatam; cypemycin; cytarabine ocfosfate; cytolytic factor; cytostatin; dacliximab; decitabine; dehydrodidemnin B; deslorelin; dexamethasone; dexifosfamide; dexrazoxane; dexverapamil; diaziquone; didemnin B; didox; diethylnorspermine; dihydro-5-azacytidine; dihydrotaxol, 9-; dioxamycin; diphenyl spiromustine; docetaxel; docosanol; dolasetron; doxifluridine; droloxifene; dronabinol; duocarmycin SA; ebselen; ecomustine; edelfosine; edrecolomab; eflornithine; elemene; emitefur; epirubicin; epristeride; estramustine analogue; estrogen agonists; estrogen antagonists; etanidazole; etoposide phosphate; exemestane; fadrozole; fazarabine; fenretinide; filgrastim; finasteride; flavopiridol; flezelastine; fluasterone; fludarabine; fluorodaunorunicin hydrochloride; forfenimex; formestane; fostriecin; fotemustine; gadolinium texaphyrin; gallium nitrate; galocitabine; ganirelix; gelatinase inhibitors; gemcitabine; glutathione inhibitors; hepsulfam; heregulin; hexamethylene bisacetamide; hypericin; ibandronic acid; idarubicin; idoxifene; idramantone; ilmofosine; ilomastat; imidazoacridones; imiquimod; immunostimulant peptides; insulin-like growth factor-I receptor inhibitor; interferon agonists; interferons; interleukins; iobenguane; iododoxorubicin; ipomeanol, 4-; iroplact; irsogladine; isobengazole; isohomohalicondrin B; itasetron; jasplakinolide; kahalalide F; lamellarin-N triacetate; lanreotide; leinamycin; lenograstim; lentinan sulfate; leptolstatin; letrozole; leukemia inhibiting factor; leukocyte alpha interferon; leuprolide+estrogen+progesterone; leuprorelin; levamisole; liarozole; linear polyamine analogue; lipophilic disaccharide peptide; lipophilic platinum compounds; lissoclinamide 7; lobaplatin; lombricine; lometrexol; lonidamine; losoxantrone; HMG-CoA reductase inhibitor (such as but not limited to, Lovastatin, Pravastatin, Fluvastatin, Statin, Simvastatin, and Atorvastatin); loxoribine; lurtotecan; lutetium texaphyrin; lysofylline; lytic peptides; maitansine; mannostatin A; marimastat; masoprocol; maspin; matrilysin inhibitors; matrix metalloproteinase inhibitors; menogaril; merbarone; meterelin; methioninase; metoclopramide; MIF inhibitor; mifepristone; miltefosine; mirimostim; mismatched double stranded RNA; mitoguazone; mitolactol; mitomycin analogues; mitonafide; mitotoxin fibroblast growth factor-saporin; mitoxantrone; mofarotene; molgramostim; monoclonal antibody, human chorionic gonadotrophin; monophosphoryl lipid A+myobacterium cell wall sk; mopidamol; multiple drug resistance gene inhibitor; multiple tumor suppressor 1-based therapy; mustard anticancer agent; mycaperoxide B; mycobacterial cell wall extract; myriaporone; N-acetyldinaline; N-substituted benzamides; nafarelin; nagrestip; naloxone+pentazocine; napavin; naphterpin; nartograstim; nedaplatin; nemorubicin; neridronic acid; neutral endopeptidase; nilutamide; nisamycin; nitric oxide modulators; nitroxide antioxidant; nitrullyn; 06-benzylguanine; octreotide; okicenone; oligonucleotides; onapristone; ondansetron; ondansetron; oracin; oral cytokine inducer; ormaplatin; osaterone; oxaliplatin; oxaunomycin; paclitaxel; paclitaxel analogues; paclitaxel derivatives; palauamine; palmitoylrhizoxin; pamidronic acid; panaxytriol; panomifene; parabactin; pazelliptine; pegaspargase; peldesine; pentosan polysulfate sodium; pentostatin; pentrozole; perflubron; perfosfamide; perillyl alcohol; phenazinomycin; phenylacetate; phosphatase inhibitors; picibanil; pilocarpine hydrochloride; pirarubicin; piritrexim; placetin A; placetin B; plasminogen activator inhibitor; platinum complex; platinum compounds; platinum-triamine complex; porfimer sodium; porfiromycin; prednisone; propyl bis-acridone; prostaglandin J2; proteasome inhibitors; protein A-based immune modulator; protein kinase C inhibitor; protein kinase C inhibitors, microalgal; protein tyrosine phosphatase inhibitors; purine nucleoside phosphorylase inhibitors; purpurins; pyrazoloacridine; pyridoxylated hemoglobin polyoxyethylene conjugate; raf antagonists; raltitrexed; ramosetron; ras farnesyl protein transferase inhibitors; ras inhibitors; ras-GAP inhibitor; retelliptine demethylated; rhenium Re 186 etidronate; rhizoxin; ribozymes; RII retinamide; rogletimide; rohitukine; romurtide; roquinimex; rubiginone B1; ruboxyl; safingol; saintopin; SarCNU; sarcophytol A; sargramostim; Sdi 1 mimetics; semustine; senescence derived inhibitor 1; sense oligonucleotides; signal transduction inhibitors; signal transduction modulators; single chain antigen binding protein; sizofiran; sobuzoxane; sodium borocaptate; sodium phenylacetate; solverol; somatomedin binding protein; sonermin; sparfosic acid; spicamycin D; spiromustine; splenopentin; spongistatin 1; squalamine; stem cell inhibitor; stem-cell division inhibitors; stipiamide; stromelysin inhibitors; sulfinosine; superactive vasoactive intestinal peptide antagonist; suradista; suramin; swainsonine; synthetic glycosaminoglycans; tallimustine; tamoxifen methiodide; tauromustine; tazarotene; tecogalan sodium; tegafur; tellurapyrylium; telomerase inhibitors; temoporfin; temozolomide; teniposide; tetrachlorodecaoxide; tetrazomine; thaliblastine; thiocoraline; thrombopoietin; thrombopoietin mimetic; thymalfasin; thymopoietin receptor agonist; thymotrinan; thyroid stimulating hormone; tin ethyl etiopurpurin; tirapazamine; titanocene bichloride; topsentin; toremifene; totipotent stem cell factor; translation inhibitors; tretinoin; triacetyluridine; triciribine; trimetrexate; triptorelin; tropisetron; turosteride; tyrosine kinase inhibitors; tyrphostins; UBC inhibitors; ubenimex; urogenital sinus-derived growth inhibitory factor; urokinase receptor antagonists; vapreotide; variolin B; vector system, erythrocyte gene therapy; velaresol; veramine; verdins; verteporfin; vinorelbine; vinxaltine; Vitaxin®; vorozole; zanoterone; zeniplatin; zilascorb; and zinostatin stimalamer. Additional anti-cancer drugs are 5-fluorouracil and leucovorin. These two agents are particularly useful when used in methods employing thalidomide and a topoisomerase inhibitor. In some embodiments, the FLT3 binding protein of the present disclosure is used in combination with gemcitabine. In some embodiments, the FLT3 binding protein as described herein is administered before, during, or after surgery.

The modality of administration of an FLT3 binding protein as described herein (e.g., an FLT3 targeting trispecific protein) or a pharmaceutical composition comprising the same, is, in some embodiment, in accord with known methods, e.g., injection or infusion by subcutaneous, intravenous, intraperitoneal, intracerebral, intradermic, intramuscular, intraocular, intraarterial, intrathecal, or intralesional routes, or by inhalation or by sustained release systems. In some embodiments the an FLT3 binding protein as described herein (e.g., an FLT3 targeting trispecific protein) or a pharmaceutical composition comprising the same is administered by infusion or by bolus injection. In some embodiments an FLT3 binding protein as described herein (e.g., an FLT3 targeting trispecific protein) or a pharmaceutical composition comprising the same is administered through the nose or lung, e.g., as a liquid or powder aerosol (lyophilized). In some embodiments an FLT3 binding protein as described herein (e.g., an FLT3 targeting trispecific protein) or a pharmaceutical composition comprising the same is administered intravenously, parenterally or subcutaneously as desired. When administered systemically, a pharmaceutical composition comprising an FLT3 binding protein as described herein (e.g., an FLT3 targeting trispecific protein) is for instance sterile, pyrogen-free and in a parenterally acceptable solution having due regard for pH, isotonicity, and stability.

Methods of Detection of FLT3 Expression and Diagnosis of FLT3 Associated Cancer

According to another embodiment of the disclosure, kits for detecting expression of FLT3 in vitro or in vivo are provided. The kits include the foregoing FLT3 binding protein (e.g., an FLT3 binding protein containing a labeled anti-FLT3 single domain antibody or antigen binding fragments thereof), and one or more compounds for detecting the label. In some embodiments, the label is selected from the group consisting of a fluorescent label, an enzyme label, a radioactive label, a nuclear magnetic resonance active label, a luminescent label, and a chromophore label.

In some cases, FLT3 expression is detected in a biological sample. The sample can be any sample, including, but not limited to, tissue from biopsies, autopsies and pathology specimens. Biological samples also include sections of tissues, for example, frozen sections taken for histological purposes. Biological samples further include body fluids, such as blood, serum, plasma, sputum, spinal fluid or urine. A biological sample is typically obtained from a mammal, such as a human or non-human primate.

In one embodiment, provided is a method of determining if a subject has cancer by contacting a sample from the subject with an anti-FLT3 single domain antibody as disclosed herein; and detecting binding of the single domain antibody to the sample. An increase in binding of the antibody to the sample as compared to binding of the antibody to a control sample identifies the subject as having cancer.

In another embodiment, provided is a method of confirming a diagnosis of cancer in a subject by contacting a sample from a subject diagnosed with cancer with an anti-FLT3 single domain antibody as disclosed herein; and detecting binding of the antibody to the sample. An increase in binding of the antibody to the sample as compared to binding of the antibody to a control sample confirms the diagnosis of cancer in the subject.

In some examples of the disclosed methods, the FLT3 single domain antibody is directly labeled. In some examples, the methods further include contacting a second antibody that specifically binds the anti-FLT3 single domain antibody with the sample; and detecting the binding of the second antibody. An increase in binding of the second antibody to the sample as compared to binding of the second antibody to a control sample detects a condition in the subject or confirms the diagnosis of cancer in the subject. In some cases, the condition is a hematologic malignancy derived from either of the two major blood cell lineages, i.e., the myeloid cell line (which produces granulocytes, erythrocytes, thrombocytes, macrophages and mast cells) or lymphoid cell line (which produces B, T, NK and plasma cells), such as all types of leukemias, lymphomas, and myelomas, e.g., AML. In some embodiments, the cancer is a neuroendocrine cancer, prostate cancer, lung cancer, stomach cancer, squamous cell carcinoma, pancreatic cancer, cholangiocarcinoma, triple negative breast cancer or ovarian cancer (such as epithelial ovarian carcinoma), or any other type of cancer that expresses FLT3. In some examples, the control sample is a sample from a subject without cancer. In particular examples, the sample is a blood or tissue sample.

In some cases, the antibody that binds (for example specifically binds) FLT3 is directly labeled with a detectable label. In another embodiment, the antibody that binds (for example, specifically binds) FLT3 (the first antibody) is unlabeled and a second antibody or other molecule that can bind the antibody that specifically binds FLT3 is labeled. A second antibody is chosen such that it is able to specifically bind the specific species and class of the first antibody. For example, if the first antibody is a llama IgG, then the secondary antibody may be an anti-llama-IgG. Other molecules that can bind to antibodies include, without limitation, Protein A and Protein G, both of which are available commercially. Suitable labels for the antibody or secondary antibody are described above, and include various enzymes, prosthetic groups, fluorescent materials, luminescent materials, magnetic agents and radioactive materials. Non-limiting examples of suitable enzymes include horseradish peroxidase, alkaline phosphatase, beta-galactosidase, or acetylcholinesterase. Non-limiting examples of suitable prosthetic group complexes include streptavidin/biotin and avidin/biotin. Non-limiting examples of suitable fluorescent materials include umbelliferon, fluorescein, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride or phycoerythrin. A non-limiting exemplary luminescent material is luminol; a non-limiting exemplary a magnetic agent is gadolinium, and non-limiting exemplary radioactive labels include 1251, 1311, 35S or 3H.

In an alternative embodiment, FLT3 can be assayed in a biological sample by a competition immunoassay utilizing FLT3 standards labeled with a detectable substance and an unlabeled antibody that specifically binds FLT3. In this assay, the biological sample, the labeled FLT3 standards and the antibody that specifically bind FLT3 are combined and the amount of labeled FLT3 standard bound to the unlabeled antibody is determined. The amount of FLT3 in the biological sample is inversely proportional to the amount of labeled FLT3 standard bound to the antibody that specifically binds FLT3.

The immunoassays and method disclosed herein can be used for a number of purposes. In one embodiment, the antibody that specifically binds FLT3 may be used to detect the production of FLT3 in cells in cell culture. In another embodiment, the antibody can be used to detect the amount of FLT3 in a biological sample, such as a tissue sample, or a blood or serum sample. In some examples, the FLT3 is cell-surface FLT3. In other examples, the FLT3 is soluble FLT3 (e.g., FLT3 in a cell culture supernatant or soluble FLT3 in a body fluid sample, such as a blood or serum sample).

In one embodiment, a kit is provided for detecting FLT3 in a biological sample, such as a blood sample or tissue sample. For example, to confirm a cancer diagnosis in a subject, a biopsy can be performed to obtain a tissue sample for histological examination. Alternatively, a blood sample can be obtained to detect the presence of soluble FLT3 protein or fragment. Kits for detecting a polypeptide will typically comprise a single domain antibody, according to the present disclosure, that specifically binds FLT3. In some embodiments, an antibody fragment, such as an scFv fragment, a VH domain, or a Fab is included in the kit. In a further embodiment, the antibody is labeled (for example, with a fluorescent, radioactive, or an enzymatic label).

In one embodiment, a kit includes instructional materials disclosing means of use of an antibody that binds FLT3. The instructional materials may be written, in an electronic form (such as a computer diskette or compact disk), may be visual (such as video files), or provided through an electronic network, for example, over the internet, World Wide Web, an intranet, or other network. The kits may also include additional components to facilitate the particular application for which the kit is designed. Thus, for example, the kit may additionally contain means of detecting a label (such as enzyme substrates for enzymatic labels, filter sets to detect fluorescent labels, appropriate secondary labels such as a secondary antibody, or the like). The kits may additionally include buffers and other reagents routinely used for the practice of a particular method. Such kits and appropriate contents are well known to those of skill in the art.

In one embodiment, the diagnostic kit comprises an immunoassay. Although the details of the immunoassays may vary with the particular format employed, the method of detecting FLT3 in a biological sample generally includes the steps of contacting the biological sample with an antibody which specifically reacts, under immunologically reactive conditions, to an FLT3 polypeptide. The antibody is allowed to specifically bind under immunologically reactive conditions to form an immune complex, and the presence of the immune complex (bound antibody) is detected directly or indirectly.

Methods of determining the presence or absence of a cell surface marker are well known in the art. For example, the antibodies can be conjugated to other compounds including, but not limited to, enzymes, magnetic beads, colloidal magnetic beads, haptens, fluorochromes, metal compounds, radioactive compounds or drugs. The antibodies can also be utilized in immunoassays such as but not limited to radioimmunoassays (RIAs), ELISA, or immunohistochemical assays. The antibodies can also be used for fluorescence activated cell sorting (FACS). FACS employs a plurality of color channels, low angle and obtuse light-scattering detection channels, and impedance channels, among other more sophisticated levels of detection, to separate or sort cells. See U.S. Pat. No. 5,061,620). Any of the single domain antibodies that bind FLT3, as disclosed herein, can be used in these assays. Thus, the antibodies can be used in a conventional immunoassay, including, without limitation, an ELISA, an RIA, FACS, tissue immunohistochemistry, Western blot or immunoprecipitation.

EXAMPLES Example 1: Screening of Phage Display Library for Identification of FLT3 Binding Domains

Llamas were immunized with purified FLT3 protein expressed in Expi293 cells. A phage display library for expression of heavy variable antibody domains was constructed from circulating B cells isolated from the immunized llamas (See van der Linden, de Geus, Stok, Bos, van Wassenaar, Verrips, and Frenken. 2000. J Immunol Methods 240:185-195). Phage clones were screened for binding to FLT3 by expressing llama anti-FLT3 proteins in E. coli, preparing periplasmic extracts, and performing colorimetric ELISAs. Seventy unique heavy chain only sequences were identified (SEQ ID Nos. 1-70) that produced a signal in the ELISA screening with human FLT3 protein (data provided in Table 2) relative to control wells that lacked FLT3 protein. The CDR1, CDR2, and CDR3 sequences for these heavy variable domains are listed in Table 1, above.

TABLE 2 Binding of Llama Anti-Human FLT3 Antibodies to Human FLT3 in an ELISA Assay (The numerical values in Table 2 represent the absorbance readings for the colorimetric ELISA) Sequence name ELISA FLT3 ELISA control FLT3/control FLL101 1.7 0.5 3 FLL103 3.8 0.1 28 FLL116 1.1 0.2 5 FLL125 2.1 0.1 17 FLL129 2.6 0.3 9 FLL137 1.8 0.2 8 FLL14 1.8 0.4 5 FLL146 0.9 0.2 4 FLL158 2.1 0.1 17 FLL179 3.7 0.2 17 FLL181 3.2 0.6 5 FLL187 1.9 0.1 18 FLL32 1.6 0.3 5 FLL51 2.9 0.2 16 FLL55 2.0 0.3 6 FLL77 4.0 0.2 22 FLL97 1.4 0.2 7 FLL21 3.3 0.2 20 FLL57 1.4 0.2 9 FLL62 0.5 0.1 5 FLL79 0.6 0.1 4 FLL86 1.9 0.1 15 FLL112 3.6 0.1 34 FLL142 4.0 0.3 15 FLL143 4.0 0.1 47 FLL154 4.0 0.5 8 FLL168 4.0 0.1 28 FLL170 4.0 0.1 38 FLL188 4.0 0.1 51 FLL40 4.0 0.2 21 FLL6 3.8 0.2 16 FLL75 4.0 0.2 19 FLL83 3.8 0.1 35 FLL94 4.0 0.8 5 FLL99 3.7 0.3 13 FLL38 4.0 0.1 45 FLL53 3.9 0.2 17 FLL553 3.7 0.1 37 FLL74 3.9 0.7 6 FLL102 3.7 0.1 37 FLL122 4.0 0.2 26 FLL134 1.3 0.1 15 FLL153 1.4 0.1 15 FLL41 0.8 0.2 5 FLL67 2.7 0.2 12 FLL92 4.0 0.2 25 FLL71 1.9 0.2 9 FLL8 3.3 0.2 14 FLL84 1.3 0.3 4 FLL107 3.8 0.3 11 FLL141 4.0 0.1 28 FLL34 4.0 0.1 39 FLL4 3.7 0.1 43 FLL61 3.9 0.2 25 FLL78 4.0 0.1 27 FLL1 3.4 0.3 11 FLL26 2.9 0.8 4 FLL160 0.7 0.1 9 FLL173 0.5 0.1 6 FLL178 4.0 0.1 48 FLL27 4.0 0.4 10 FLL190 4.0 0.1 43 FLL43 2.0 0.2 12 FLL15 2.5 0.1 31 FLL45 4.0 0.1 28 FLL39 1.9 0.2 12 FLL177 4.0 0.1 54 FLL823 3.6 0.9 4 FLL76 0.5 0.1 5 FLL822 4.0 0.2 17

Example 2: Incorporation of FLT3 Binding Heavy Chain Only Single Domain Antibodies into FLT3 Targeting Multispecific Proteins and T Cell Dependent Cellular Cytotoxicity Assays

The anti-FLT3 antibody sequences were cloned into DNA constructs for expression of recombinant multispecific proteins (SEQ ID Nos. 196-266). The coding sequences of the multispecific proteins contained a signal peptide for secreted cell expression, one of the anti-FLT3 antibody variable domains (SEQ ID Nos. 1-70), a humanized single domain anti-albumin antibody variable domain (SEQ ID No. 372), a humanized anti-CD3 antibody scFv fragment (SEQ ID No. 373), and a repeat of six histidine sequences (SEQ ID No. 374). A linker sequence was inserted at the junctions between the antibody domains (SEQ ID No. 375). These anti-FLT3/anti-albumin/anti-CD3 multispecific protein constructs were transfected into Expi293 cells (Life Technologies). The amount of multispecific protein in the conditioned media from the transfected Expi293 cells was quantitated using by using an Octet instrument with Protein A tips using a multispecific protein of similar molecular weight to the anti-FLT3/anti-albumin/anti-CD3 proteins as a standard.

The conditioned media were tested in a T-cell dependent cellular cytotoxicity assay (See Nazarian A A, Archibeque I L, Nguyen Y H, Wang P, Sinclair A M, Powers D A. 2015. J Biomol Screen. 20:519-27). In this assay, luciferase labelled MV-4-11 cells (biphenotypic B myelomonocytic leukemia cell line, ATCC® CRL-9591™), which express FLT3, were combined with purified human T cells and a titration of anti-FLT3/anti-albumin/anti-CD3 multispecific protein. If a multispecific protein directs T cells to kill the MV-4-11 cells, the signal in a luciferase assay performed at 48 hours after starting the experiment should decrease. FIGS. 1-11 show graphs of TDCC viability results. EC₅₀ values from the TDCC assay are listed in Tables 3 and 4. The most potent molecule had an EC₅₀ value of 3 pM. A negative control for the TDCC assays was an anti-GFP/anti-albumin/anti-CD3 protein, and this protein did not direct the T cells to kills the MV-4-11 cells except for slight activity at the highest concentration tested (e.g., FIGS. 10 and 21). As the multispecific proteins contain an anti-albumin domain, TDCC assay were also performed in the presence of 15 mg/ml human serum albumin (HSA) to measure directed T cell killing while bound to albumin (FIGS. 12-21). For all of the FLT3-targeting multispecific proteins tested, the EC₅₀ values for directed T cell killing increased in the presence of HSA (Table 3), and also relative to EC50 values for directed T cell killing in the presence of bovine serum albumin (BSA) (FIGS. 1-11 and Tables 3 and 4). The anti-albumin domain in the multispecific proteins does not bind to BSA (data not shown).

TABLE 3 EC₅₀ Values for Redirected T Cell Killing of MV-4-11 Cells by Anti- FLT3/Anti-Albumin/Anti-CD3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences (n/a indicates insufficient activity to calculate an EC₅₀ using the protein concentrations tested) FLT3 Binder EC₅₀ (pM) EC₅₀ with HSA (pM) FLL21 169 1182 FLL57 384 3119 FLL62 619 6816 FLL1 56  888 FLL103 141 1355 FLL107 11  85 FLL112 136 1330 FLL125 330 1717 FLL129 1168 n/a FLL137 705 n/a FLL14 257 1147 FLL141 16  77 FLL142 233  984 FLL143 70  345 FLL146 989 5678 FLL15 108  613 FLL154 152  818 FLL158 546 1973 FLL160 n/a n/a FLL168 77  383 FLL173 n/a n/a FLL177 n/a n/a FLL178 n/a n/a FLL179 176 1162 FLL190 37  239 FLL26 136 1186 FLL32 175 1172 FLL34 17  170 FLL38 104  814 FLL39 1387 n/a FLL4 21  181 FLL40 69  601 FLL43 223 1478 FLL45 407 n/a FLL51 906 4649 FLL53 n/a n/a FLL55 192 1077 FLL6 201 1859 FLL61 39  424 FLL75 224 2102 FLL76 n/a n/a FLL77 224 1582 FLL78 21  194 FLL82 1185 n/a FLL822 n/a n/a FLL83 134 1274 FLL94 202 2836 FLL99 202 1746

TABLE 4 EC₅₀ Values for Redirected T Cell Killing of MV-4-11 Cells by Anti-FLT3/Anti-Albumin/Anti-CD3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences FLT3 Binder EC₅₀ with BSA (pM) EC₅₀ with HSA (pM) FLL8 26 680 FLL41 380 2200 FLL71 83 1900 FLL92 3 53 FLL134 66 1700 FLL153 150 3000

Example 3: Humanized Anti-FLT3 Binding Heavy Chain Only Single Domain Antibodies and Multispecific Proteins Containing the Same

Seven of the llama anti-FLT3 antibody sequences were humanized by grafting their CDR sequences onto human germline sequences, while retaining some llama framework sequences to ensure the antibodies did not lose activity (SEQ ID Nos. 71-76; 389-390). These eight humanized sequences were cloned into expression constructs for expression of anti-FLT3/anti-albumin/anti-CD3 multispecific proteins (SEQ ID Nos. 267-272; 391-392) in CHO cells. The constructs were stably transfected into CHO cells, and pools of stable transfectants were used to express the multispecific proteins. Affinity and multi modal chromatography were used to purify the multispecific proteins from the CHO conditioned media. An SDS-PAGE of the purified proteins (FIG. 23) shows the proteins were purified to greater than 95% purity. The purified proteins were also analyzed by analytical size exclusion chromatography and were found to be 99% monomer (data not shown). These purified proteins were tested in a TDCC assay as described in Example 2 using FLT3-expressing MV-4-11 (acute myeloid leukemia cell line) and EOL1 cells (acute myeloid (eosinophilic) leukemia cell line). The assays were run in the presence 15 mg/ml BSA or 15 mg/ml HSA to measure directed cell killing while bound to albumin. Because the anti-albumin domain in these multispecific proteins does not measurably bind to BSA, BSA served as a negative control for the addition of HSA. The results of these TDCC assays are plotted in FIGS. 24-27 and FIGS. 38-39, and the EC₅₀ values for directed T cell killing are listed in Table 5 and Table 6. The MV-4-11 data in FIGS. 24-25 and FIGS. 38-39 and the corresponding EC₅₀ values in Tables 5 and 6 represent the results of assays performed using T cells isolated from two different T cell donors. Potent directed T cell killing was observed with both cell lines in the absence of HSA, with EC₅₀ values ranging from 1.6 pM to 22 pM. With addition of HSA, the EC₅₀ values increased, ranging from 10 pM to 408 pM. The purified proteins were also tested in a TDCC assay with FLT3-expression THP1 cells (acute monocytic leukemia) in the absence or presence of 15 mg/ml HSA (FIGS. 30 and 31) with FLT3-expressing MOLM13 (acute myeloid leukemia) and HL60 (human leukemia) cells (FIGS. 32 and 33) in the presence of 15 mg/ml HSA. The EC₅₀ values calculated from these TDCC assay data are also listed in Table 5. With the THP1 cells, EC₅₀ values ranged from 23 pM to 268 pM in the absence of HSA and 46 pM to 856 pM in the presence of HSA. With the MOLM13 cells in the presence of HSA the EC₅₀ values ranged from 30 pM to 229 pM, and with HL60 cells in the presence of HSA the EC₅₀ values ranged from 551 pM to 5478 pM. Compared to all of the other cell lines, the potency of FLT3 TriTAC directed T cell killing with HL60 cells was less potent. It is expected that if viability of the HL60 cells had been measured at a later time point, for example 72 or 96 hours, that the magnitude of killing would have been greater and that killing would have been more potent. A negative control anti-GFP/anti-albumin/anti-CD3 protein had no activity in these TDCC assays except for a minor amount of killing at the highest concentrations tested (>10 nM).

TABLE 5 EC₅₀ Values for Redirected T Cell Killing of MV-4-11, EOL1, THP1, MOLM13, and HL60 Cells by Purified Anti-FLT3/Anti-Albumin/Anti-CD3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences EOL1 + MV-4-11 + THP1 + MOLM-13 + HL60 + EOL1 HSA MV-4-11 HSA THP1 HSA HSA HSA FLT3 EC₅₀ EC₅₀ EC₅₀ EC₅₀ EC₅₀ EC₅₀ EC₅₀ EC₅₀ Binder (pM) (pM) (pM) (pM) (pM) (pM) (pM) (pM) FLH107 1.6 10 5.9 47 23 46 30 551 FLH141 3.5 24 9.6 119 25 118 54 1634 FLH19C 9.4 47 16 184 155 458 90 1518 FLH34 3 22 8.5 91 28 127 47 1027 FLH4 4.2 27 9.7 90 38 179 69 1828 FLH78 5.2 35 12 101 51 221 97 1702 FLH92a not tested not tested not tested not tested 268 856 188 3876 FLH92b not tested not tested not tested not tested 109 461 229 5478

TABLE 6 EC₅₀ Values for Redirected T Cell Killing of MV-4-11 Cells by Purified Anti-FLT3/Anti-Albumin/Anti-CD3 Multispecific Proteins Containing Humanized Anti-FLT3 Sequences FLT3 Binder MV-4-11 EC₅₀ (pM) MV-4-11 + HSA EC₅₀ (pM) FLH107 2.4 90 FLH141 1.7 45 FLH19C 6.9 224 FLH34 2 124 FLH4 1.9 92 FLH78 2.2 104 FLH92a 22 408 FLH92b 17 390

Example 4: Affinity Determinations for Anti-FLT3 Multispecific Proteins

The affinities of the purified multispecific proteins for human and cynomolgus FLT3 were measured with an Octet instrument with streptavidin tips were loaded with biotinylated human or cynomolgus FLT3 protein. The tips were then incubated with solutions containing 50, 16.7, 5.6, or 1.9 nM of the multispecific protein. Affinities (K_(D)), listed in Table 7, were calculated by measuring the on rate and off rate of binding of anti-FLT3/anti-albumin/anti-CD3 multispecific proteins to the captured biotinylated FLT3 proteins. The multispecific proteins bound to human FLT3 with affinities ranging from 0.7 to 8.1 nM, and they bound to cynomolgus FLT3 with affinities ranging from 2.7 to 214 nM.

TABLE 7 Affinities of Purified Anti-FLT3/Anti-Albumin/Anti- CD3 Multispecific Proteins Containing Humanized Anti- FLT3 Sequences for Human or Cynomolgus Monkey FLT3 Human K_(D) Cynomolgus K_(D) Cyno/human FLT3 Binder (nM) (nM) (fold change) FLH107 0.7 10 14.3 FLH19C 1.9 2.7 1.4 FLH141 1.9 35 18.4 FLH34 2.1 19 9.0 FLH4 3.7 214 57.8 FLH78 4.1 161 39.3 FLH92a 8.1 11.8 1.5 FLH92b 4.9 7.8 1.6

Additional affinity determinations were performed using conditioned media from Example 2 with known concentrations of anti-FLT3/anti-CD3 multispecific proteins. The multispecific proteins tested contain llama anti-FLT3 sequences FLL8, FLL41, FLL71, FLL92, FLL134, or FLL153. An Octet instrument with streptavidin tips were loaded with biotinylated human or cynomolgus FLT3 protein, and K_(D) values for binding FLT3 were calculated by measuring the on rate and off rate of binding of anti-FLT3/anti-CD3 multispecific proteins to the biotinylated FLT3 proteins. The affinity measurements were made using a single 50 nM concentration of anti-FLT3/anti-CD3 multispecific proteins, which allowed for rank ordering potency. The measured relative affinities are listed in Table 8. The multispecific proteins bound to human FLT3 with K_(D) values ranging from 1.4 to 41 nM to cynomolgus FLT3 with K_(D) values ranging from 2 to 102 nM.

TABLE 8 Relative affinities of Purified Anti-FLT3/Anti-Albumin/Anti- CD3 Multispecific Proteins Containing Llama Anti-FLT3 Sequences for Human or Cynomolgus Monkey FLT3 Human K_(D) Cynomolgus K_(D) Cyno/human FLT3 Binder (nM) (nM) (fold change) FLL8 9.3 18 1.9 FLL41 31 34 1.1 FLL71 18 26 1.4 FLL92 1.4 2 1.4 FLL134 18 24 1.3 FLL153 41 102 2.5

Example 5: Tumor Regression and Inhibition in an Orthotopic EOL1 Xenograft Model

In vivo efficacy study of an exemplary FLT3 targeted multispecific protein of this disclosure is performed with EOL1, expressing luciferase and GFP, orthotopic model. EOL1 LucGFP cells are injected intravenously through the tail vein into 6-8 weeks old female Nod/Scid/IL2Rg−/− (NSG) animals. Intraperitoneal injection of D-luciferin, followed by anesthesia with isofluorane and subsequent whole body bioluminescence imaging (BLI) is to enable monitoring of tumor burden. Bioluminescent signals emitted by the interaction between luciferase expressed by the tumor cells and luciferin are captured by imaging and quantified as total flux (photons/sec) using. When the total flux reaches an average of 15E6 for all animals, the animals are injected through bolus tail vein with expanded T cells from PBMC. Briefly, pan-T cells are activated with a suitable human T Cell Activation/Expansion Kit. After three days, IL2 is added every two days until day 11. Cells are harvested, activation/expansion beads are magnetically removed, and cells are washed and resuspended in PBS. 2-days post T cell injection, mice are imaged as described above and animals are randomized into groups.

Three days post T-cell implant, a single dose of an FLT3 targeted multispecific protein of this disclosure and a negative control GFP targeted multispecific protein is administered via bolus tail vein injection. Animals are sacrificed when they exhibit hindlimb paralysis, an endpoint for AML orthotopic model. It is expected that the FLT3 targeted multispecific protein will result in tumor regression in a dose-dependent manner.

Example 6: Pharmacokinetics and Pharmacodynamics of FLT3 TriTACs in Cynomolgus Monkeys

A FLT3 TriTAC (SEQ ID NO: 269, containing the FLT3 binder FLH19C, SEQ ID NO: 73) was administered at doses of 10, 100, and 1000 μg/kg single i.v. bolus doses to cynomolgus monkeys, with two test subjects per dose group. This FLT3 TriTAC binds to cynomolgus FLT3 (see Table 7) and binds to cynomolgus CD3 and cynomolgus serum albumin, with affinities of 3.3 nM and 4.4 nM, respectively, as determined using biolayer interferometry (data not shown). The amount of FLT3 TriTAC present in serum samples collected at different time points after dosing was measured using an electrochemiluminescent ELISA assay using labeled antibodies recognizing the anti-ALB and anti-CD3 domains of the FLT3 TriTAC molecule as capture and detection reagents. The measured serum concentrations versus time and dose are plotted in FIG. 34. The pharmacokinetic properties calculated from these data are listed in Table 9.

TABLE 9 Pharmacokinetic Properties of a FLT3 TriTAC Dosed in Cynomolgus Monkeys T_(max) C_(max) AUC₁₆₈ AUC_(INF) Half-life Cl Vz Dose (h) (nM) (h*nM) (h*nM) (h) (μg/(h*nM)) (ug/(nM)) 10 μg/kg 0.5 5.44 279 373 85.9 0.0805 10.0 100 μg/kg 0.5 94.1 4520 5450 75.4 0.0555 6.06 1,000 μg/kg 2 846 35600 61200 147 0.0493 10.4

To determine if the FLT3 TriTAC directed cynomolgus T cells to kill endogenous cynomolgus FLT3-expressing cells, soluble FLT3L in serum and FLT3 RNA in whole blood were measured in sample collected from the pharmacokinetic study described above. Depletion of FLT3-expressing cells was expected to result in an increase in soluble FLT3L (see Brauchle et al. Mol Cancer Ther 2020; 19:1875-88). An electrochemiluminescent ELISA specific for Non-Human Primate FLT3L (Meso Scale Discovery) was used to measure the levels of FLT3L in serum samples collected at different time points (FIG. 35). With the 100 and 1,000 μg/kg dose groups, the soluble FLT3L increased over the time course of the study. One of the two subjects in the 10 μg/kg dose group had a slight increase in FLT3L at the 72 and 144 hour times points that returned to pre-dose levels at the 336 hour time point. If FLT3 expressing cells are depleted from whole blood or bone marrow, then FLT3 transcripts were expected to be depleted from RNA purified from whole blood or bone marrow. RNA was purified from whole blood or bone marrow using kits (Qiagen), cDNA was prepared by a reverse transcriptase reaction, and qPCR was used to measure the amount of FLT3 present using a standard curve qPCR method. FNTA was used as a house keeping gene for the qPCR reactions. Plotted in FIG. 36 are FTL3 RNA levels normalized to FNTA for blood samples isolated from the 100 and 1,000 μg/kg groups. Plotted in FIG. 37 are FTL3 RNA levels normalized to FNTA for bone marrow samples isolated from the 100 and 1,000 μg/kg groups. Compared to samples collected prior to dosing, FLT3 RNA is greatly reduced at all time points measured. The combined FLT3L and FLT3 RNA data indicate that the FLT3 TriTAC, when dosed at 100 and 1,000 μg/kg, eliminated FLT3 expressing cells in cynomolgus monkeys.

While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

SEQUENCES SEQ ID Sequence Seq. NO. descriptor name Amino acid sequence 1 FLT3 antibody FLL101 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRDNA KNTVYLQMNNLKPEDTAVYYCRVLSYWGQGTQVTVSS 2 FLT3 antibody FLL103 QVQLQESGGGLVQAGGSLRLSCEASGPTFSINYIDWY variable domain RQAPGKQREWVAQITRDSNSFYADSVKGRFAVSRDNA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 3 FLT3 antibody FLL116 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 4 FLT3 antibody FLL125 QVQLQESGGGLVQAGGSLRLSCAASGSTFSRNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 5 FLT3 antibody FLL129 QVQLQESGGGLVQAGGSLRLSCAASGVTFSASYIDWY variable domain RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 6 FLT3 antibody FLL137 QVQLQESGGGLVQAGGSLRLSCAASGSTFNNYAMDWF variable domain RQAPGKQREWVAQITRDSSSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 7 FLT3 antibody FLL14 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRLLSYWGQGTQVTVSS 8 FLT3 antibody FLL146 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDDTSFYADSVKGRFAISRDNA KNTVYLQMNNLRPEDTAVYYCRLLSFWGQGTQVTVSS 9 FLT3 antibody FLL158 QVQLQESGGGLVQPGGSLRLSCAASGSTFGRNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 10 FLT3 antibody FLL179 QVQLQESGGGLVQAGGSLRLSCKASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDGSSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRILSDWGQGTQVTVSS 11 FLT3 antibody FLL181 QVQLQESGGGLVQAGDSLRLSCAASGVTFSASYIDWY variable domain RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 12 FLT3 antibody FLL187 QVQLQESGGGLVQPGGSLRLSCAASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRENA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 13 FLT3 antibody FLL32 QVQLQESGGGLVQAGGSLRLSCQASGVTFNINYIDWY variable domain RQAPGRQREWVAQITRDSTRFYADSVKGRFAISRDNA KNMVYLQLNSLKPEDTAVYYCRILSYWGQGTQVTVSS 14 FLT3 antibody FLL51 QVQLQESGGGLVQPGGSLRLSCAASGFDFSISYIDWY variable domain RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRILSYWGQGTQVTVSS 15 FLT3 antibody FLL55 QVQLQESGGGLVQAGGSLRLSCAASGSTFSRNYIDWY variable domain RQAPGKQREWVAQITSAGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 16 FLT3 antibody FLL77 QVQLQESGGGLVQPGGSLRLSCAASGVTFSISYIDWY variable domain RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA KNTVYLQMNSLKPEDTAVYYCRILSYWGQGTQVTVSS 17 FLT3 antibody FLL97 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY variable domain RQAPGKQREWVAQITRDSNSFYADSVKGRFAVSRDNA KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS 18 FLT3 antibody FLL21 QVQLQESGGGLVQPGGSLTLSCAASGSTFSRNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 19 FLT3 antibody FLL57 QVQLQESGGGLVQAGGSLRLSCAASGSTFSKNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 20 FLT3 antibody FLL62 QVQLQESGGGLVQAGGSLRLSCAASGSTSSRNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 21 FLT3 antibody FLL79 QVQLQESGGGLVQAGGSLRLSCSASGSTFSRNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 22 FLT3 antibody FLL86 QVQLQESGGGLVQPGDPLRLSCAASGSTFSRNYIDWY variable domain RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS 23 FLT3 antibody FLL112 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWAGGRTHYEDSVKGRFTIHRDN AKNTVYLQMNSLKPEDTAVYYCAAQVSRAYDGIWYSG GDYWGQGTQVTVSS 24 FLT3 antibody FLL142 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWDGGRTHYADFVKGRFTISRDN AKNTVYLQMNSLKPEDTAVYYCAAQVARAYDSKWYSG GDYWGQGTQVTVSS 25 FLT3 antibody FLL143 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWVGGRTHYADSVKGRFTISRDN AKNTVYLQMNSLKPEDTAVYYCAAQVARAYDGNWYSG GDYWGQGTQVTVSS 26 FLT3 antibody FLL154 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWSGGRTHYADSVKGRFTISRDN AKNTVYLQMNSLKPEDTAVYYCAGQVARAYDGNWYSR GDYWGQGTQVTVSS 27 FLT3 antibody FLL168 QVQLQESGGGSVQAGGSLRLSCAFSGRTFSGFGTGWF variable domain RQAPEKEREFVAAISWDGGRTHYADSVKGRFTISRDN AKNTVYLQMDSLKPEDTAIYYCAAQVSRAYDGRWYSA VDYWGRGTQVTVSS 28 FLT3 antibody FLL170 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN AKNTVYLQMNSLKPEDTAVYYCAGQVARAYDSSWYSR GDYWGQGTQVTVSS 29 FLT3 antibody FLL188 QVQLQESGGGLVQAGGSLGLSCAVSGRTFSGFGTGWF variable domain RQPPEKEREFVAAISWDGGRTHYADSVKGRFTISRDN AKNTVFLQMNSLKPEDTAVYYCAAQVARAYDSRWYSG GDYWGQGTQVTVSS 30 FLT3 antibody FLL40 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN AKNTVSLVYLQMNSLKPDDTAVYYCAGQVARAYDSSW YSRGDYLGQGTQVTVSS 31 FLT3 antibody FLL6 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWDGGRTHYADSVKGRFTISRDN AANTVYLQMNSLKPEDTAVYYCAGQVSRAYDSMWYGR DDYWGQGTQVTVSS 32 FLT3 antibody FLL75 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN AKNTVNLVYLQMNDLRPEDTAVYYCAGQVARAYDSNW YSRGDYWGQGTQVTVSS 33 FLT3 antibody FLL83 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN AENTVYLEMNSLKPEDTAVYICAGQVSRAYDSNWYSR DDYWGQGTQVTVSS 34 FLT3 antibody FLL94 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPEKEREFVAAISWDGGRTHYADSVKGRFTISRDN AKNTVYLQMNSLKPEDTAIYYCAGQVARAYDTRWYSR GDYWGQGTQVTVSS 35 FLT3 antibody FLL99 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWDGGRTHYADFVKGRFTISRDN AKNTVYLQMNSLKPEDTAVYYCAAQVARAYDSRWYSG GDYWGQGTQVTVSS 36 FLT3 antibody FLL38 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAVSWSGGTTEIADSVKGRFTISRDN AKNTVYLQMSSLKPGDTAVYYCAGQVARAYDSRWYSR GDYWGQGTQVTVSS 37 FLT3 antibody FLL53 QVQLQESGGGLVQAGDSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAVSQSGGTTHYADSVKGRFTISRDN AKNTETLVYLQMNSLKPEDTAVYYCAGQVARAYDSSW YARGDYWGQGTQVTVSS 38 FLT3 antibody FLL553 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN AKNTVNLVYLQMNSLRPEDTAVYYCAGQVARAYDSNW YSRGDYWGQGTQVTVSS 39 FLT3 antibody FLL74 QVQLQESGGGLVQAGGSLRLSCRFSGRTFSGFGTGWF variable domain RQAPGKEREFVAAISWAGGRTHYEDSVKGRFTISRDN AKNTVYLQMNSLKPEDTAVYYCAVQVSRAYDGIWYSG GDYWGQGTQVTVSS 40 FLT3 antibody FLL102 QVQLQESGGGLVQAGGSLMVSCAASGGTWSSYATGWF variable domain RQVPGKERKLIAGISRSGGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTSSVVYTSG NDYDYWGQGTQVTVSS 41 FLT3 antibody FLL122 QVQLQESGGGLVQAGGSLMVSCAASGGTWSSYATGWF variable domain RQVPGKERELIAGISRSGGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTSSVVYTSG NDYDYWGQGTQVTVSS 42 FLT3 antibody FLL134 QVQLQESGGGLVQPGGSLRLSCAASGGTFSSYATGWF variable domain RQVPGKEREFIAGISRNSGRTYAESVKGRFTISRDNA KNTVYLQMNTLRPDDTAVYYCAAARYFTRDAIYTSGD DYDYWGQGTQVTASS 43 FLT3 antibody FLL153 QVQLQESGGGLVQVGGSLMVSCAASGGTFSSYATGWF variable domain RQVPGKEREFIAGVSRNSGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTGVYYCAAARYFTRDAVYTSG DDYDYWGQGTQVTVSS 44 FLT3 antibody FLL41 QVQLQESGGGLVQLGDSLMVSCAASGGTFSSYATGWF variable domain RQVPGREREFIAGISRSGGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTTSVVYTSG DDYDYWGQGTQVTVSS 45 FLT3 antibody FLL67 QVQLQESGGGLVQLGDSLMVSCAASGGTFSSYATGWF variable domain RQVPGKEREFIAGISRSGGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTTSVVYTSG DDYDYWGQGTQVTVSS 46 FLT3 antibody FLL92 QVQLQESGGGLVQAGGSLMVSCAASGGTWSSYATGWF variable domain RQVPGKERELIAGISRSGGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKSDDTAVYYCAAARYFTSSVVYTSG NDYDYWGQGTQVTVSS 47 FLT3 antibody FLL71 QVQLQESGGGLVQVGGSLMVSCAASGGTFSSYATGWF variable domain RQVPGKEREFIAGISRNSGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTRDAVYTSG DDYDYWGQGTQVTVSS 48 FLT3 antibody FLL8 QVQLQESGGGLVQVGGSLMVSCAASGGTFSSYATGWF variable domain RQVPGKEREFIAGISRNSGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTRDVVYTSG DDYDYWGQGTQVTVSS 49 FLT3 antibody FLL84 QVQLQESGGGLVQAGGSLMVSCAASGGTFSSYATGWF variable domain RQVPGKEREFIAGISRSGGRTYYAESVKGRFTISRDN AKNTVYLQMNTLKPDDTAVYYCAAARYFTTSVVYTSG DDYDYWGQGTQVTVSS 50 FLT3 antibody FLL107 QVQLQESGGGLVQAGGSLRLSCAASGRTFSSYAMGWF variable domain RQAPGKEREFVAAISWSGSNTYYADSVKGRFTISRDN AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSS 51 FLT3 antibody FLL141 QVQLQESGGGLVQAGGSLRLSCAASGRTFSSYAMGWF variable domain RQAPGMEREFVAAISWSGYSTYYADSVKGRFTISRDD AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSS 52 FLT3 antibody FLL34 QVQLQESGGGLVQAGGSLRLSCAASGRTFSSYALGWF variable domain RQAPGKEREFVAAISWSGGNTYYADSVKGRFTISRDD AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSS 53 FLT3 antibody FLL4 QVQLQESGGGLVQAGGSLRLSCAASERTFSSYTMGWF variable domain RQAPGKEREFVAAMSWSGGSTYYADSVKGRFTISRDN AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSS 54 FLT3 antibody FLL61 QVQLQESGGGLVQAGGSLRLSCAASERTFSSYAMGWF variable domain RQAPGKEREFVAAISWSGGSTYYADSVKGRFTISRDN AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPI VKYWGQGTQVTVSS 55 FLT3 antibody FLL78 QVQLQESGGGWVQAGGSLRLSCAASGRTFSSYAMGWF variable domain RQAPGKEREFVAAISWSGSSTYYADSVKGRFTISRDN AKNTVYLLMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSS 56 FLT3 antibody FLL1 QVQLQESGGGLVQAGGSLRLSCAASGRTFSTLTVAWF variable domain RQAPGKEREFVVASIPSGSNTGYAESVKGRFTISRDI AKNTVYLQMNSLKPEDTAMYFCAARIYFGSSRGYDYW GQGTQVTVSS 57 FLT3 antibody FLL26 QVQLQESGGGLVQAGGSLRLSCAASGRTFTTYTVAWF variable domain RQAPGKEREFLVASIPTGSNTAYAESVKGRFTISRGN AKNTVYLQMNSLKPEDTAMYYCAARTYFGSSRGYDYW GQGTQVTVSS 58 FLT3 antibody FLL160 QVQLQESGGGLVQAGDSLRLSCATSGRTFNLYRVGWF variable domain RQAPGKEREFVARITWSADITQYADSVKGRFTISRDN AKNTVYLQMNSLKPEDTAIYYCATTLRKSSGIYHVDD YDDWGQGTQVTVSS 59 FLT3 antibody FLL173 QVQLQESGGGLVQAGGSLRLSCATSGRTFNLYRVGWF variable domain RQAPGKEREFVARITWSADITQYTDSVKGRFTISRDN AKNTVYLQMNSLKPEDTAIYYCATTLRKSSGIYHTDD YDYWGQGTQVTVSS 60 FLT3 antibody FLL178 QVQLQESGGGLVQPGGSLRLSCAASGFTFSDYAMSWV variable domain RQAPGKGLEWVSGISSGGYKIGYTDSTKGRFTISRDN AKNTLYLQMNSLTAEDTAVYYCAKGTQWSWSLRDNTS RGQGTQVTVSS 61 FLT3 antibody FLL27 QVQLQESGGGLVQPGGSLRLSCKASGFTFSSYAMSWV variable domain RQAPGKGLEWVSGISSGGYKIGYTDSTKGRFTISRDN AKNTLYLQMNSLNAEDTAVYYCAKGTQWSWALRDSTS RGQGTQVTVSS 62 FLT3 antibody FLL190 QVQLQESGGGLVQAGGSLTLSCTASGSTFSINHFSWY variable domain RQAPGKQRELVAFISSDGVSIDVESVKGRFTISGDND KNTAYLQMNGLKPEDTAVYYCYYRGFWGQGTQVTVSS 63 FLT3 antibody FLL43 QVQLQESGGGLVQPGGSLTLSCTASGSTFSINHFAWY variable domain RQAPGKQRELVAFISSDGRSTDVESVKGRFTISGDND KNTAYLQMNGLKPEDTAVYYCYYRGSWGQGTQVTVSS 64 FLT3 antibody FLL15 QVQLQESGGGLVQAGGSLSLSCAASEGTISHAAMGWF variable domain RQAPGKERQFVAYDTWTGGSTNYADSVKDRFTITGDH AKNTVYLQMNSLKPEDTGVYYCAVRGRYSASYTYTNP ASYKYWGQGTQVTVSS 65 FLT3 antibody FLL45 QVQLQESGGGLVQAGGSLRLSCAASGGTFSSSAMGWF variable domain RQAPGKEREFVATITQNDVPTYYTHSVKGRFTISRDN AKNTMYLQMNSLKPEDTAVYYCAQRVAQASGWRTTIK DYGYWGQGTQVTVSS 66 FLT3 antibody FLL39 QVQLQESGGGLVQAGGSLRLSCAASGLTSSTYRMAWF variable domain RQAPGKEREFAAGISYSADSGGSTNYADSVKGRFTIS RDNAKNTVYLQMSSLKPEDTAVYYCAAGRYSGTYNSP YSSSYVYWGQGTQVTVSS 67 FLT3 antibody FLL177 QVQLQESGGGLVQTGGSLRLSCAASGSTFSRNTMGWF variable domain RQAPGKERVFVLGISWSGIRSYYLDSAKARFTISRDN AKNTVYLQMNSLRPEDTAVYYCAAQEGSSPGPYKYWG QGTQVTVSS 68 FLT3 antibody FLL823 QVQLQESGGGVVQVGGSLRLSCAASGGTFGYYAVGWF variable domain RQAPGKEREFVAAVTWNGAYLYSDPVKGRFTISRDNA KNTVYLQMNSLKSEDTAVYYCGLDRWSAVVESTPSTR GQGTQVTVSS 69 FLT3 antibody FLL76 QVQLQESGGGLVQAGGSLRLSCAASGGAFSSYVMGWF variable domain RQAPGKEREFVAAVISWSGRITDYADSVKGRFSISRD NAKSTVYLQMNNLKPEDTAVYYCAAKTGMYIDLRTST FDYWGQGTQVTVSS 70 FLT3 antibody FLL822 QVQLQESGGGSVQAGGSLRLSCTASGRTFTDYTMGWF variable domain RQAPGKEREFMLGISSNGYRRYYTGSMKDRFTISRDN VKKTVYLQMNDLKPEDTAVYYCAASEDHGAPRYDYWG QGTQVTVSS 71 FLT3 antibody FLH107 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYAMGWF variable domain RQAPGKEREFVAAISWSGSNTYYADSVKGRFTISRDN SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSS 72 FLT3 antibody FLH141 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYAMGWF variable domain RQAPGMEREFVAAISWSGYSTYYADSVKGRFTISRDN SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSS 73 FLT3 antibody FLH19C EVQLVESGGGLVQPGGSLTLSCAASGSTFSINHFSWY variable domain RQAPGKQRELVAFISSDGVSIDVESVKGRFTISGDNS KNTAYLQMNSLRAEDTAVYYCYYRGFWGQGTLVTVSS 74 FLT3 antibody FLH34 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYALGWF variable domain RQAPGKEREFVAAISWSGGNTYYADSVKGRFTISRDN SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSS 75 FLT3 antibody FLH4 EVQLLESGGGLVQPGGSLTLSCAASERTFSSYTMGWF variable domain RQAPGKEREFVAAMSWSGGSTYYADSVKGRFTISRDN SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSS 76 FLT3 antibody FLH78 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYAMGWF variable domain RQAPGKEREFVAAISWSGSSTYYADSVKGRFTISRDN SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSS 77 CDR1 FLL101 GVTFSINYID 78 CDR1 FLL103 GPTFSINYID 77 CDR1 FLL116 GVTFSINYID 79 CDR1 FLL125 GSTFSRNYID 80 CDR1 FLL129 GVTFSASYID 81 CDR1 FLL137 GSTFNNYAMD 77 CDR1 FLL14 GVTFSINYID 77 CDR1 FLL146 GVTFSINYID 82 CDR1 FLL158 GSTFGRNYID 77 CDR1 FLL179 GVTFSINYID 80 CDR1 FLL181 GVTFSASYID 77 CDR1 FLL187 GVTFSINYID 83 CDR1 FLL32 GVTFNINYID 84 CDR1 FLL51 GFDFSISYID 79 CDR1 FLL55 GSTFSRNYID 85 CDR1 FLL77 GVTFSISYID 77 CDR1 FLL97 GVTFSINYID 79 CDR1 FLL21 GSTFSRNYID 86 CDR1 FLL57 GSTFSKNYID 87 CDR1 FLL62 GSTSSRNYID 79 CDR1 FLL79 GSTFSRNYID 79 CDR1 FLL86 GSTFSRNYID 88 CDR1 FLL112 GRTFSGFGTG 88 CDR1 FLL142 GRTFSGFGTG 88 CDR1 FLL143 GRTFSGFGTG 88 CDR1 FLL154 GRTFSGFGTG 88 CDR1 FLL168 GRTFSGFGTG 88 CDR1 FLL170 GRTFSGFGTG 88 CDR1 FLL188 GRTFSGFGTG 88 CDR1 FLL40 GRTFSGFGTG 88 CDR1 FLL6 GRTFSGFGTG 88 CDR1 FLL75 GRTFSGFGTG 88 CDR1 FLL83 GRTFSGFGTG 88 CDR1 FLL94 GRTFSGFGTG 88 CDR1 FLL99 GRTFSGFGTG 88 CDR1 FLL38 GRTFSGFGTG 88 CDR1 FLL53 GRTFSGFGTG 88 CDR1 FLL553 GRTFSGFGTG 88 CDR1 FLL74 GRTFSGFGTG 89 CDR1 FLL102 GGTWSSYATG 89 CDR1 FLL122 GGTWSSYATG 90 CDR1 FLL134 GGTFSSYATG 90 CDR1 FLL153 GGTFSSYATG 90 CDR1 FLL41 GGTFSSYATG 90 CDR1 FLL67 GGTFSSYATG 89 CDR1 FLL92 GGTWSSYATG 90 CDR1 FLL71 GGTFSSYATG 90 CDR1 FLL8 GGTFSSYATG 90 CDR1 FLL84 GGTFSSYATG 91 CDR1 FLL107 GRTFSSYAMG 91 CDR1 FLL141 GRTFSSYAMG 92 CDR1 FLL34 GRTFSSYALG 93 CDR1 FLL4 ERTFSSYTMG 94 CDR1 FLL61 ERTFSSYAMG 91 CDR1 FLL78 GRTFSSYAMG 95 CDR1 FLL1 GRTFSTLTVA 96 CDR1 FLL26 GRTFTTYTVA 97 CDR1 FLL160 GRTFNLYRVG 97 CDR1 FLL173 GRTFNLYRVG 98 CDR1 FLL178 GFTFSDYAMS 99 CDR1 FLL27 GFTFSSYAMS 100 CDR1 FLL190 GSTFSINHFS 101 CDR1 FLL43 GSTFSINHFA 102 CDR1 FLL15 EGTISHAAMG 103 CDR1 FLL45 GGTFSSSAMG 104 CDR1 FLL39 GLTSSTYRMA 105 CDR1 FLL177 GSTFSRNTMG 106 CDR1 FLL823 GGTFGYYAVG 107 CDR1 FLL76 GGAFSSYVMG 108 CDR1 FLL822 GRTFTDYTMG 91 CDR1 FLH107 GRTFSSYAMG 91 CDR1 FLH141 GRTFSSYAMG 100 CDR1 FLH19C GSTFSINHFS 92 CDR1 FLH34 GRTFSSYALG 93 CDR1 FLH4 ERTFSSYTMG 91 CDR1 FLH78 GRTFSSYAMG 109 CDR2 FLL101 QITRDSNSFYADSVKG 109 CDR2 FLL103 QITRDSNSFYADSVKG 109 CDR2 FLL116 QITRDSNSFYADSVKG 110 CDR2 FLL125 QITSGGNTHYEPSLKG 111 CDR2 FLL129 QITRGGDSFYADSVKG 112 CDR2 FLL137 QITRDSSSFYADSVKG 109 CDR2 FLL14 QITRDSNSFYADSVKG 113 CDR2 FLL146 QITRDDTSFYADSVKG 110 CDR2 FLL158 QITSGGNTHYEPSLKG 114 CDR2 FLL179 QITRDGSSFYADSVKG 111 CDR2 FLL181 QITRGGDSFYADSVKG 109 CDR2 FLL187 QITRDSNSFYADSVKG 115 CDR2 FLL32 QITRDSTRFYADSVKG 111 CDR2 FLL51 QITRGGDSFYADSVKG 116 CDR2 FLL55 QITSAGNTHYEPSLKG 111 CDR2 FLL77 QITRGGDSFYADSVKG 109 CDR2 FLL97 QITRDSNSFYADSVKG 110 CDR2 FLL21 QITSGGNTHYEPSLKG 110 CDR2 FLL57 QITSGGNTHYEPSLKG 110 CDR2 FLL62 QITSGGNTHYEPSLKG 110 CDR2 FLL79 QITSGGNTHYEPSLKG 110 CDR2 FLL86 QITSGGNTHYEPSLKG 117 CDR2 FLL112 AISWAGGRTHYEDSVKG 118 CDR2 FLL142 AISWDGGRTHYADFVKG 119 CDR2 FLL143 AISWVGGRTHYADSVKG 120 CDR2 FLL154 AISWSGGRTHYADSVKG 121 CDR2 FLL168 AISWDGGRTHYADSVKG 122 CDR2 FLL170 AISWSGGTTHYADSVKG 121 CDR2 FLL188 AISWDGGRTHYADSVKG 122 CDR2 FLL40 AISWSGGTTHYADSVKG 121 CDR2 FLL6 AISWDGGRTHYADSVKG 122 CDR2 FLL75 AISWSGGTTHYADSVKG 122 CDR2 FLL83 AISWSGGTTHYADSVKG 121 CDR2 FLL94 AISWDGGRTHYADSVKG 118 CDR2 FLL99 AISWDGGRTHYADFVKG 123 CDR2 FLL38 AVSWSGGTTEIADSVKG 124 CDR2 FLL53 AVSQSGGTTHYADSVKG 122 CDR2 FLL553 AISWSGGTTHYADSVKG 117 CDR2 FLL74 AISWAGGRTHYEDSVKG 125 CDR2 FLL102 GISRSGGRTYYAESVKG 125 CDR2 FLL122 GISRSGGRTYYAESVKG 126 CDR2 FLL134 GISRNSGRTYAESVKG 127 CDR2 FLL153 GVSRNSGRTYYAESVKG 125 CDR2 FLL41 GISRSGGRTYYAESVKG 125 CDR2 FLL67 GISRSGGRTYYAESVKG 125 CDR2 FLL92 GISRSGGRTYYAESVKG 128 CDR2 FLL71 GISRNSGRTYYAESVKG 128 CDR2 FLL8 GISRNSGRTYYAESVKG 125 CDR2 FLL84 GISRSGGRTYYAESVKG 129 CDR2 FLL107 AISWSGSNTYYADSVKG 130 CDR2 FLL141 AISWSGYSTYYADSVKG 131 CDR2 FLL34 AISWSGGNTYYADSVKG 132 CDR2 FLL4 AMSWSGGSTYYADSVKG 133 CDR2 FLL61 AISWSGGSTYYADSVKG 134 CDR2 FLL78 AISWSGSSTYYADSVKG 135 CDR2 FLL1 ASIPSGSNTGYAESVKG 136 CDR2 FLL26 ASIPTGSNTAYAESVKG 137 CDR2 FLL160 RITWSADITQYADSVKG 138 CDR2 FLL173 RITWSADITQYTDSVKG 139 CDR2 FLL178 GISSGGYKIGYTDSTKG 139 CDR2 FLL27 GISSGGYKIGYTDSTKG 140 CDR2 FLL190 FISSDGVSIDVESVKG 141 CDR2 FLL43 FISSDGRSTDVESVKG 142 CDR2 FLL15 YDTWTGGSTNYADSVKD 143 CDR2 FLL45 TITQNDVPTYYTHSVKG 144 CDR2 FLL39 AGISYSADSGGSTNYADSVKG 145 CDR2 FLL177 GISWSGIRSYYLDSAKA 146 CDR2 FLL823 AVTWNGAYLYSDPVKG 147 CDR2 FLL76 AVISWSGRITDYADSVKG 148 CDR2 FLL822 GISSNGYRRYYTGSMKD 149 CDR2 FLH107 ISWSGSNTYYADSVKG 150 CDR2 FLH141 ISWSGYSTYYADSVKG 151 CDR2 FLH19C ISSDGVSIDVESVKG 152 CDR2 FLH34 ISWSGGNTYYADSVKG 153 CDR2 FLH4 MSWSGGSTYYADSVKG 154 CDR2 FLH78 ISWSGSSTYYADSVKG 155 CDR3 FLL101 LSY 155 CDR3 FLL103 LSY 155 CDR3 FLL116 LSY 156 CDR3 FLL125 LDY 155 CDR3 FLL129 LSY 155 CDR3 FLL137 LSY 155 CDR3 FLL14 LSY 157 CDR3 FLL146 LSF 156 CDR3 FLL158 LDY 158 CDR3 FLL179 LSD 155 CDR3 FLL181 LSY 155 CDR3 FLL187 LSY 155 CDR3 FLL32 LSY 155 CDR3 FLL51 LSY 156 CDR3 FLL55 LDY 155 CDR3 FLL77 LSY 155 CDR3 FLL97 LSY 156 CDR3 FLL21 LDY 156 CDR3 FLL57 LDY 156 CDR3 FLL62 LDY 156 CDR3 FLL79 LDY 156 CDR3 FLL86 LDY 159 CDR3 FLL112 AQVSRAYDGIWYSGGDY 160 CDR3 FLL142 AQVARAYDSKWYSGGDY 161 CDR3 FLL143 AQVARAYDGNWYSGGDY 162 CDR3 FLL154 GQVARAYDGNWYSRGDY 163 CDR3 FLL168 AQVSRAYDGRWYSAVDY 164 CDR3 FLL170 GQVARAYDSSWYSRGDY 165 CDR3 FLL188 AQVARAYDSRWYSGGDY 164 CDR3 FLL40 GQVARAYDSSWYSRGDY 166 CDR3 FLL6 GQVSRAYDSMWYGRDDY 167 CDR3 FLL75 GQVARAYDSNWYSRGDY 168 CDR3 FLL83 GQVSRAYDSNWYSRDDY 169 CDR3 FLL94 GQVARAYDTRWYSRGDY 165 CDR3 FLL99 AQVARAYDSRWYSGGDY 170 CDR3 FLL38 GQVARAYDSRWYSRGDY 171 CDR3 FLL53 GQVARAYDSSWYARGDY 167 CDR3 FLL553 GQVARAYDSNWYSRGDY 172 CDR3 FLL74 VQVSRAYDGIWYSGGDY 173 CDR3 FLL102 ARYFTSSVVYTSGNDYDY 173 CDR3 FLL122 ARYFTSSVVYTSGNDYDY 174 CDR3 FLL134 ARYFTRDAIYTSGDDYDY 175 CDR3 FLL153 ARYFTRDAVYTSGDDYDY 176 CDR3 FLL41 ARYFTTSVVYTSGDDYDY 176 CDR3 FLL67 ARYFTTSVVYTSGDDYDY 173 CDR3 FLL92 ARYFTSSVVYTSGNDYDY 175 CDR3 FLL71 ARYFTRDAVYTSGDDYDY 177 CDR3 FLL8 ARYFTRDVVYTSGDDYDY 176 CDR3 FLL84 ARYFTTSVVYTSGDDYDY 178 CDR3 FLL107 AGGSTRVVVTTTPVVKY 178 CDR3 FLL141 AGGSTRVVVTTTPVVKY 178 CDR3 FLL34 AGGSTRVVVTTTPVVKY 178 CDR3 FLL4 AGGSTRVVVTTTPVVKY 179 CDR3 FLL61 AGGSTRVVVTTTPIVKY 178 CDR3 FLL78 AGGSTRVVVTTTPVVKY 180 CDR3 FLL1 RIYFGSSRGYDY 181 CDR3 FLL26 RTYFGSSRGYDY 182 CDR3 FLL160 TLRKSSGIYHVDDYDD 183 CDR3 FLL173 TLRKSSGIYHTDDYDY 184 CDR3 FLL178 GTQWSWSLRDNTS 185 CDR3 FLL27 GTQWSWALRDSTS 186 CDR3 FLL190 RGF 187 CDR3 FLL43 RGS 188 CDR3 FLL15 RGRYSASYTYTNPASYKY 189 CDR3 FLL45 RVAQASGWRTTIKDYGY 190 CDR3 FLL39 GRYSGTYNSPYSSSYVY 191 CDR3 FLL177 AQEGSSPGPYKY 192 CDR3 FLL823 DRWSAVVESTPST 193 CDR3 FLL76 AKTGMYIDLRTSTFDY 194 CDR3 FLL822 SEDHGAPRYDY 195 CDR3 FLH107 GGSTRVVVTTTPVVKY 195 CDR3 FLH141 GGSTRVVVTTTPVVKY 186 CDR3 FLH19C RGF 195 CDR3 FLH34 GGSTRVVVTTTPVVKY 195 CDR3 FLH4 GGSTRVVVTTTPVVKY 195 CDR3 FLH78 GGSTRVVVTTTPVVKY 273 framework 1 FLL101 QVQLQESGGGLVQAGGSLRLSCAAS 274 framework 1 FLL103 QVQLQESGGGLVQAGGSLRLSCEAS 273 framework 1 FLL116 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL125 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL129 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL137 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL14 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL146 QVQLQESGGGLVQAGGSLRLSCAAS 275 framework 1 FLL158 QVQLQESGGGLVQPGGSLRLSCAAS 276 framework 1 FLL179 QVQLQESGGGLVQAGGSLRLSCKAS 277 framework 1 FLL181 QVQLQESGGGLVQAGDSLRLSCAAS 275 framework 1 FLL187 QVQLQESGGGLVQPGGSLRLSCAAS 278 framework 1 FLL32 QVQLQESGGGLVQAGGSLRLSCQAS 275 framework 1 FLL51 QVQLQESGGGLVQPGGSLRLSCAAS 273 framework 1 FLL55 QVQLQESGGGLVQAGGSLRLSCAAS 275 framework 1 FLL77 QVQLQESGGGLVQPGGSLRLSCAAS 273 framework 1 FLL97 QVQLQESGGGLVQAGGSLRLSCAAS 279 framework 1 FLL21 QVQLQESGGGLVQPGGSLTLSCAAS 273 framework 1 FLL57 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL62 QVQLQESGGGLVQAGGSLRLSCAAS 280 framework 1 FLL79 QVQLQESGGGLVQAGGSLRLSCSAS 281 framework 1 FLL86 QVQLQESGGGLVQPGDPLRLSCAAS 282 framework 1 FLL112 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL142 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL143 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL154 QVQLQESGGGLVQAGGSLRLSCAVS 283 framework 1 FLL168 QVQLQESGGGSVQAGGSLRLSCAFS 282 framework 1 FLL170 QVQLQESGGGLVQAGGSLRLSCAVS 284 framework 1 FLL188 QVQLQESGGGLVQAGGSLGLSCAVS 282 framework 1 FLL40 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL6 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL75 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL83 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL94 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL99 QVQLQESGGGLVQAGGSLRLSCAVS 282 framework 1 FLL38 QVQLQESGGGLVQAGGSLRLSCAVS 285 framework 1 FLL53 QVQLQESGGGLVQAGDSLRLSCAVS 282 framework 1 FLL553 QVQLQESGGGLVQAGGSLRLSCAVS 286 framework 1 FLL74 QVQLQESGGGLVQAGGSLRLSCRFS 287 framework 1 FLL102 QVQLQESGGGLVQAGGSLMVSCAAS 287 framework 1 FLL122 QVQLQESGGGLVQAGGSLMVSCAAS 275 framework 1 FLL134 QVQLQESGGGLVQPGGSLRLSCAAS 288 framework 1 FLL153 QVQLQESGGGLVQVGGSLMVSCAAS 289 framework 1 FLL41 QVQLQESGGGLVQLGDSLMVSCAAS 289 framework 1 FLL67 QVQLQESGGGLVQLGDSLMVSCAAS 287 framework 1 FLL92 QVQLQESGGGLVQAGGSLMVSCAAS 288 framework 1 FLL71 QVQLQESGGGLVQVGGSLMVSCAAS 288 framework 1 FLL8 QVQLQESGGGLVQVGGSLMVSCAAS 287 framework 1 FLL84 QVQLQESGGGLVQAGGSLMVSCAAS 273 framework 1 FLL107 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL141 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL34 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL4 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL61 QVQLQESGGGLVQAGGSLRLSCAAS 290 framework 1 FLL78 QVQLQESGGGWVQAGGSLRLSCAAS 273 framework 1 FLL1 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL26 QVQLQESGGGLVQAGGSLRLSCAAS 291 framework 1 FLL160 QVQLQESGGGLVQAGDSLRLSCATS 292 framework 1 FLL173 QVQLQESGGGLVQAGGSLRLSCATS 275 framework 1 FLL178 QVQLQESGGGLVQPGGSLRLSCAAS 293 framework 1 FLL27 QVQLQESGGGLVQPGGSLRLSCKAS 294 framework 1 FLL190 QVQLQESGGGLVQAGGSLTLSCTAS 295 framework 1 FLL43 QVQLQESGGGLVQPGGSLTLSCTAS 296 framework 1 FLL15 QVQLQESGGGLVQAGGSLSLSCAAS 273 framework 1 FLL45 QVQLQESGGGLVQAGGSLRLSCAAS 273 framework 1 FLL39 QVQLQESGGGLVQAGGSLRLSCAAS 297 framework 1 FLL177 QVQLQESGGGLVQTGGSLRLSCAAS 298 framework 1 FLL823 QVQLQESGGGVVQVGGSLRLSCAAS 273 framework 1 FLL76 QVQLQESGGGLVQAGGSLRLSCAAS 299 framework 1 FLL822 QVQLQESGGGSVQAGGSLRLSCTAS 300 framework 1 FLH107 EVQLLESGGGLVQPGGSLTLSCAAS 300 framework 1 FLH141 EVQLLESGGGLVQPGGSLTLSCAAS 301 framework 1 FLH19C EVQLVESGGGLVQPGGSLTLSCAAS 300 framework 1 FLH34 EVQLLESGGGLVQPGGSLTLSCAAS 300 framework 1 FLH4 EVQLLESGGGLVQPGGSLTLSCAAS 300 framework 1 FLH78 EVQLLESGGGLVQPGGSLTLSCAAS 302 framework 2 FLL101 WYRQAPGKQREWVA 302 framework 2 FLL103 WYRQAPGKQREWVA 302 framework 2 FLL116 WYRQAPGKQREWVA 302 framework 2 FLL125 WYRQAPGKQREWVA 303 framework 2 FLL129 WYRQAPGNEREWVA 304 framework 2 FLL137 WFRQAPGKQREWVA 302 framework 2 FLL14 WYRQAPGKQREWVA 302 framework 2 FLL146 WYRQAPGKQREWVA 302 framework 2 FLL158 WYRQAPGKQREWVA 302 framework 2 FLL179 WYRQAPGKQREWVA 303 framework 2 FLL181 WYRQAPGNEREWVA 302 framework 2 FLL187 WYRQAPGKQREWVA 305 framework 2 FLL32 WYRQAPGRQREWVA 303 framework 2 FLL51 WYRQAPGNEREWVA 302 framework 2 FLL55 WYRQAPGKQREWVA 303 framework 2 FLL77 WYRQAPGNEREWVA 302 framework 2 FLL97 WYRQAPGKQREWVA 302 framework 2 FLL21 WYRQAPGKQREWVA 302 framework 2 FLL57 WYRQAPGKQREWVA 302 framework 2 FLL62 WYRQAPGKQREWVA 302 framework 2 FLL79 WYRQAPGKQREWVA 302 framework 2 FLL86 WYRQAPGKQREWVA 306 framework 2 FLL112 WFRQAPGKEREFVA 306 framework 2 FLL142 WFRQAPGKEREFVA 306 framework 2 FLL143 WFRQAPGKEREFVA 306 framework 2 FLL154 WFRQAPGKEREFVA 307 framework 2 FLL168 WFRQAPEKEREFVA 306 framework 2 FLL170 WFRQAPGKEREFVA 308 framework 2 FLL188 WFRQPPEKEREFVA 306 framework 2 FLL40 WFRQAPGKEREFVA 306 framework 2 FLL6 WFRQAPGKEREFVA 306 framework 2 FLL75 WFRQAPGKEREFVA 306 framework 2 FLL83 WFRQAPGKEREFVA 307 framework 2 FLL94 WFRQAPEKEREFVA 306 framework 2 FLL99 WFRQAPGKEREFVA 306 framework 2 FLL38 WFRQAPGKEREFVA 306 framework 2 FLL53 WFRQAPGKEREFVA 306 framework 2 FLL553 WFRQAPGKEREFVA 306 framework 2 FLL74 WFRQAPGKEREFVA 406 framework 2 FLL102 WFRQVPGKERKLIA 309 framework 2 FLL122 WFRQVPGKERELIA 310 framework 2 FLL134 WFRQVPGKEREFIA 310 framework 2 FLL153 WFRQVPGKEREFIA 311 framework 2 FLL41 WFRQVPGREREFIA 310 framework 2 FLL67 WFRQVPGKEREFIA 309 framework 2 FLL92 WFRQVPGKERELIA 310 framework 2 FLL71 WFRQVPGKEREFIA 310 framework 2 FLL8 WFRQVPGKEREFIA 310 framework 2 FLL84 WFRQVPGKEREFIA 306 framework 2 FLL107 WFRQAPGKEREFVA 312 framework 2 FLL141 WFRQAPGMEREFVA 306 framework 2 FLL34 WFRQAPGKEREFVA 306 framework 2 FLL4 WFRQAPGKEREFVA 306 framework 2 FLL61 WFRQAPGKEREFVA 306 framework 2 FLL78 WFRQAPGKEREFVA 313 framework 2 FLL1 WFRQAPGKEREFVV 314 framework 2 FLL26 WFRQAPGKEREFLV 306 framework 2 FLL160 WFRQAPGKEREFVA 306 framework 2 FLL173 WFRQAPGKEREFVA 315 framework 2 FLL178 WVRQAPGKGLEWVS 315 framework 2 FLL27 WVRQAPGKGLEWVS 316 framework 2 FLL190 WYRQAPGKQRELVA 316 framework 2 FLL43 WYRQAPGKQRELVA 317 framework 2 FLL15 WFRQAPGKERQFVA 306 framework 2 FLL45 WFRQAPGKEREFVA 318 framework 2 FLL39 WFRQAPGKEREFA 319 framework 2 FLL177 WFRQAPGKERVFVL 306 framework 2 FLL823 WFRQAPGKEREFVA 306 framework 2 FLL76 WFRQAPGKEREFVA 320 framework 2 FLL822 WFRQAPGKEREFML 321 framework 2 FLH107 WFRQAPGKEREFVAA 322 framework 2 FLH141 WFRQAPGMEREFVAA 407 framework 2 FLH19C WYRQAPGKQRELVAF 321 framework 2 FLH34 WFRQAPGKEREFVAA 321 framework 2 FLH4 WFRQAPGKEREFVAA 321 framework 2 FLH78 WFRQAPGKEREFVAA 323 framework 3 FLL101 RFAISRDNAKNTVYLQMNNLKPEDTAVYYCRV 324 framework 3 FLL103 RFAVSRDNAKNTVYLQMNSLKPEDTAVYYCRV 325 framework 3 FLL116 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRV 326 framework 3 FLL125 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 325 framework 3 FLL129 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRV 325 framework 3 FLL137 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRV 327 framework 3 FLL14 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRL 328 framework 3 FLL146 RFAISRDNAKNTVYLQMNNLRPEDTAVYYCRL 326 framework 3 FLL158 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 329 framework 3 FLL179 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRI 325 framework 3 FLL181 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRV 330 framework 3 FLL187 RFAISRENAKNTVYLQMNSLKPEDTAVYYCRV 331 framework 3 FLL32 RFAISRDNAKNMVYLQLNSLKPEDTAVYYCRI 329 framework 3 FLL51 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRI 326 framework 3 FLL55 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 329 framework 3 FLL77 RFAISRDNAKNTVYLQMNSLKPEDTAVYYCRI 324 framework 3 FLL97 RFAVSRDNAKNTVYLQMNSLKPEDTAVYYCRV 326 framework 3 FLL21 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 326 framework 3 FLL57 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 326 framework 3 FLL62 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 326 framework 3 FLL79 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 326 framework 3 FLL86 RFTISRDNAKNTAYLQMNSLKPEDTAVYYCRI 332 framework 3 FLL112 RFTIHRDNAKNTVYLQMNSLKPEDTAVYYCA 333 framework 3 FLL142 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCA 333 framework 3 FLL143 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCA 333 framework 3 FLL154 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCA 334 framework 3 FLL168 RFTISRDNAKNTVYLQMDSLKPEDTAIYYCA 333 framework 3 FLL170 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCA 335 framework 3 FLL188 RFTISRDNAKNTVFLQMNSLKPEDTAVYYCA 336 framework 3 FLL40 RFTISRDNAKNTVSLVYLQMNSLKPDDTAVYYCA 337 framework 3 FLL6 RFTISRDNAANTVYLQMNSLKPEDTAVYYCA 338 framework 3 FLL75 RFTISRDNAKNTVNLVYLQMNDLRPEDTAVYYCA 339 framework 3 FLL83 RFTISRDNAENTVYLEMNSLKPEDTAVYICA 340 framework 3 FLL94 RFTISRDNAKNTVYLQMNSLKPEDTAIYYCA 333 framework 3 FLL99 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCA 341 framework 3 FLL38 RFTISRDNAKNTVYLQMSSLKPGDTAVYYCA 342 framework 3 FLL53 RFTISRDNAKNTETLVYLQMNSLKPEDTAVYYCA 343 framework 3 FLL553 RFTISRDNAKNTVNLVYLQMNSLRPEDTAVYYCA 333 framework 3 FLL74 RFTISRDNAKNTVYLQMNSLKPEDTAVYYCA 344 framework 3 FLL102 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 344 framework 3 FLL122 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 345 framework 3 FLL134 RFTISRDNAKNTVYLQMNTLRPDDTAVYYCAA 346 framework 3 FLL153 RFTISRDNAKNTVYLQMNTLKPDDTGVYYCAA 344 framework 3 FLL41 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 344 framework 3 FLL67 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 347 framework 3 FLL92 RFTISRDNAKNTVYLQMNTLKSDDTAVYYCAA 344 framework 3 FLL71 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 344 framework 3 FLL8 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 344 framework 3 FLL84 RFTISRDNAKNTVYLQMNTLKPDDTAVYYCAA 348 framework 3 FLL107 RFTISRDNAKNTVYLQMDSLKPEDTAVYYCA 349 framework 3 FLL141 RFTISRDDAKNTVYLQMDSLKPEDTAVYYCA 349 framework 3 FLL34 RFTISRDDAKNTVYLQMDSLKPEDTAVYYCA 348 framework 3 FLL4 RFTISRDNAKNTVYLQMDSLKPEDTAVYYCA 348 framework 3 FLL61 RFTISRDNAKNTVYLQMDSLKPEDTAVYYCA 350 framework 3 FLL78 RFTISRDNAKNTVYLLMDSLKPEDTAVYYCA 351 framework 3 FLL1 RFTISRDIAKNTVYLQMNSLKPEDTAMYFCAA 352 framework 3 FLL26 RFTISRGNAKNTVYLQMNSLKPEDTAMYYCAA 353 framework 3 FLL160 RFTISRDNAKNTVYLQMNSLKPEDTAIYYCAT 353 framework 3 FLL173 RFTISRDNAKNTVYLQMNSLKPEDTAIYYCAT 354 framework 3 FLL178 RFTISRDNAKNTLYLQMNSLTAEDTAVYYCAK 355 framework 3 FLL27 RFTISRDNAKNTLYLQMNSLNAEDTAVYYCAK 356 framework 3 FLL190 RFTISGDNDKNTAYLQMNGLKPEDTAVYYCYY 356 framework 3 FLL43 RFTISGDNDKNTAYLQMNGLKPEDTAVYYCYY 357 framework 3 FLL15 RFTITGDHAKNTVYLQMNSLKPEDTGVYYCAV 358 framework 3 FLL45 RFTISRDNAKNTMYLQMNSLKPEDTAVYYCAQ 359 framework 3 FLL39 RFTISRDNAKNTVYLQMSSLKPEDTAVYYCAA 360 framework 3 FLL177 RFTISRDNAKNTVYLQMNSLRPEDTAVYYCA 361 framework 3 FLL823 RFTISRDNAKNTVYLQMNSLKSEDTAVYYCGL 362 framework 3 FLL76 RFSISRDNAKSTVYLQMNNLKPEDTAVYYCA 363 framework 3 FLL822 RFTISRDNVKKTVYLQMNDLKPEDTAVYYCAA 364 framework 3 FLH107 RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAA 364 framework 3 FLH141 RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAA 365 framework 3 FLH19C RFTISGDNSKNTAYLQMNSLRAEDTAVYYCYY 364 framework 3 FLH34 RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAA 364 framework 3 FLH4 RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAA 364 framework 3 FLH78 RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAA 366 framework 4 FLL101 WGQGTQVTVSS 366 framework 4 FLL103 WGQGTQVTVSS 366 framework 4 FLL116 WGQGTQVTVSS 366 framework 4 FLL125 WGQGTQVTVSS 366 framework 4 FLL129 WGQGTQVTVSS 366 framework 4 FLL137 WGQGTQVTVSS 366 framework 4 FLL14 WGQGTQVTVSS 366 framework 4 FLL146 WGQGTQVTVSS 366 framework 4 FLL158 WGQGTQVTVSS 366 framework 4 FLL179 WGQGTQVTVSS 366 framework 4 FLL181 WGQGTQVTVSS 366 framework 4 FLL187 WGQGTQVTVSS 366 framework 4 FLL32 WGQGTQVTVSS 366 framework 4 FLL51 WGQGTQVTVSS 366 framework 4 FLL55 WGQGTQVTVSS 366 framework 4 FLL77 WGQGTQVTVSS 366 framework 4 FLL97 WGQGTQVTVSS 366 framework 4 FLL21 WGQGTQVTVSS 366 framework 4 FLL57 WGQGTQVTVSS 366 framework 4 FLL62 WGQGTQVTVSS 366 framework 4 FLL79 WGQGTQVTVSS 366 framework 4 FLL86 WGQGTQVTVSS 366 framework 4 FLL112 WGQGTQVTVSS 366 framework 4 FLL142 WGQGTQVTVSS 366 framework 4 FLL143 WGQGTQVTVSS 366 framework 4 FLL154 WGQGTQVTVSS 367 framework 4 FLL168 WGRGTQVTVSS 366 framework 4 FLL170 WGQGTQVTVSS 366 framework 4 FLL188 WGQGTQVTVSS 368 framework 4 FLL40 LGQGTQVTVSS 366 framework 4 FLL6 WGQGTQVTVSS 366 framework 4 FLL75 WGQGTQVTVSS 366 framework 4 FLL83 WGQGTQVTVSS 366 framework 4 FLL94 WGQGTQVTVSS 366 framework 4 FLL99 WGQGTQVTVSS 366 framework 4 FLL38 WGQGTQVTVSS 366 framework 4 FLL53 WGQGTQVTVSS 366 framework 4 FLL553 WGQGTQVTVSS 366 framework 4 FLL74 WGQGTQVTVSS 366 framework 4 FLL102 WGQGTQVTVSS 366 framework 4 FLL122 WGQGTQVTVSS 369 framework 4 FLL134 WGQGTQVTASS 366 framework 4 FLL153 WGQGTQVTVSS 366 framework 4 FLL41 WGQGTQVTVSS 366 framework 4 FLL67 WGQGTQVTVSS 366 framework 4 FLL92 WGQGTQVTVSS 366 framework 4 FLL71 WGQGTQVTVSS 366 framework 4 FLL8 WGQGTQVTVSS 366 framework 4 FLL84 WGQGTQVTVSS 366 framework 4 FLL107 WGQGTQVTVSS 366 framework 4 FLL141 WGQGTQVTVSS 366 framework 4 FLL34 WGQGTQVTVSS 366 framework 4 FLL4 WGQGTQVTVSS 366 framework 4 FLL61 WGQGTQVTVSS 366 framework 4 FLL78 WGQGTQVTVSS 366 framework 4 FLL1 WGQGTQVTVSS 366 framework 4 FLL26 WGQGTQVTVSS 366 framework 4 FLL160 WGQGTQVTVSS 366 framework 4 FLL173 WGQGTQVTVSS 370 framework 4 FLL178 RGQGTQVTVSS 370 framework 4 FLL27 RGQGTQVTVSS 366 framework 4 FLL190 WGQGTQVTVSS 366 framework 4 FLL43 WGQGTQVTVSS 366 framework 4 FLL15 WGQGTQVTVSS 366 framework 4 FLL45 WGQGTQVTVSS 366 framework 4 FLL39 WGQGTQVTVSS 366 framework 4 FLL177 WGQGTQVTVSS 370 framework 4 FLL823 RGQGTQVTVSS 366 framework 4 FLL76 WGQGTQVTVSS 366 framework 4 FLL822 WGQGTQVTVSS 371 framework 4 FLH107 WGQGTLVTVSS 371 framework 4 FLH141 WGQGTLVTVSS 371 framework 4 FLH19C WGQGTLVTVSS 371 framework 4 FLH34 WGQGTLVTVSS 371 framework 4 FLH4 WGQGTLVTVSS 371 framework 4 FLH78 WGQGTLVTVSS 196 anti-FLT3/anti- FLL101 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRDNA protein KNTVYLQMNNLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 197 anti-FLT3/anti- FLL103 QVQLQESGGGLVQAGGSLRLSCEASGPTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSNSFYADSVKGRFAVSRDNA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 198 anti-FLT3/anti- FLL116 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 199 anti-FLT3/anti- FLL125 QVQLQESGGGLVQAGGSLRLSCAASGSTFSRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 200 anti-FLT3/anti- FLL129 QVQLQESGGGLVQAGGSLRLSCAASGVTFSASYIDWY HSA/anti-CD3 fusion RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 201 anti-FLT3/anti- FLL137 QVQLQESGGGLVQAGGSLRLSCAASGSTFNNYAMDWF HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSSSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 202 anti-FLT3/anti- FLL14 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRLLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 203 anti-FLT3/anti- FLL146 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDDTSFYADSVKGRFAISRDNA protein KNTVYLQMNNLRPEDTAVYYCRLLSFWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 204 anti-FLT3/anti- FLL158 QVQLQESGGGLVQPGGSLRLSCAASGSTFGRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 205 anti-FLT3/anti- FLL179 QVQLQESGGGLVQAGGSLRLSCKASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDGSSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRILSDWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 206 anti-FLT3/anti- FLL181 QVQLQESGGGLVQAGDSLRLSCAASGVTFSASYIDWY HSA/anti-CD3 fusion RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 207 anti-FLT3/anti- FLL187 QVQLQESGGGLVQPGGSLRLSCAASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSNSFYADSVKGRFAISRENA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 208 anti-FLT3/anti- FLL32 QVQLQESGGGLVQAGGSLRLSCQASGVTFNINYIDWY HSA/anti-CD3 fusion RQAPGRQREWVAQITRDSTRFYADSVKGRFAISRDNA protein KNMVYLQLNSLKPEDTAVYYCRILSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 209 anti-FLT3/anti- FLL51 QVQLQESGGGLVQPGGSLRLSCAASGFDFSISYIDWY HSA/anti-CD3 fusion RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRILSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 210 anti-FLT3/anti- FLL55 QVQLQESGGGLVQAGGSLRLSCAASGSTFSRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSAGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 211 anti-FLT3/anti- FLL77 QVQLQESGGGLVQPGGSLRLSCAASGVTFSISYIDWY HSA/anti-CD3 fusion RQAPGNEREWVAQITRGGDSFYADSVKGRFAISRDNA protein KNTVYLQMNSLKPEDTAVYYCRILSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 212 anti-FLT3/anti- FLL97 QVQLQESGGGLVQAGGSLRLSCAASGVTFSINYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITRDSNSFYADSVKGRFAVSRDNA protein KNTVYLQMNSLKPEDTAVYYCRVLSYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 213 anti-FLT3/anti- FLL21 QVQLQESGGGLVQPGGSLTLSCAASGSTFSRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 214 anti-FLT3/anti- FLL57 QVQLQESGGGLVQAGGSLRLSCAASGSTFSKNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 215 anti-FLT3/anti- FLL62 QVQLQESGGGLVQAGGSLRLSCAASGSTSSRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 216 anti-FLT3/anti- FLL79 QVQLQESGGGLVQAGGSLRLSCSASGSTFSRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 217 anti-FLT3/anti- FLL86 QVQLQESGGGLVQPGDPLRLSCAASGSTFSRNYIDWY HSA/anti-CD3 fusion RQAPGKQREWVAQITSGGNTHYEPSLKGRFTISRDNA protein KNTAYLQMNSLKPEDTAVYYCRILDYWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 218 anti-FLT3/anti- FLL112 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWAGGRTHYEDSVKGRFTIHRDN protein AKNTVYLQMNSLKPEDTAVYYCAAQVSRAYDGIWYSG GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 219 anti-FLT3/anti- FLL142 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWDGGRTHYADFVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAVYYCAAQVARAYDSKWYSG GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 220 anti-FLT3/anti- FLL143 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWVGGRTHYADSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAVYYCAAQVARAYDGNWYSG GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 221 anti-FLT3/anti- FLL154 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGRTHYADSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAVYYCAGQVARAYDGNWYSR GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 222 anti-FLT3/anti- FLL168 QVQLQESGGGSVQAGGSLRLSCAFSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPEKEREFVAAISWDGGRTHYADSVKGRFTISRDN protein AKNTVYLQMDSLKPEDTAIYYCAAQVSRAYDGRWYSA VDYWGRGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 223 anti-FLT3/anti- FLL170 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAVYYCAGQVARAYDSSWYSR GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 224 anti-FLT3/anti- FLL188 QVQLQESGGGLVQAGGSLGLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQPPEKEREFVAAISWDGGRTHYADSVKGRFTISRDN protein AKNTVFLQMNSLKPEDTAVYYCAAQVARAYDSRWYSG GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 225 anti-FLT3/anti- FLL40 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN protein AKNTVSLVYLQMNSLKPDDTAVYYCAGQVARAYDSSW YSRGDYLGQGTQVTVSSGGGGSGGGSEVQLVESGGGL VQPGNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWV SSISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNS LRPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGG GSEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAIN WVRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTI SRDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYI SYWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQ EPSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPG QAPRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGV QPEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 226 anti-FLT3/anti- FLL6 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWDGGRTHYADSVKGRFTISRDN protein AANTVYLQMNSLKPEDTAVYYCAGQVSRAYDSMWYGR DDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 227 anti-FLT3/anti- FLL75 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN protein AKNTVNLVYLQMNDLRPEDTAVYYCAGQVARAYDSNW YSRGDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGL VQPGNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWV SSISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNS LRPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGG GSEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAIN WVRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTI SRDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYI SYWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQ EPSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPG QAPRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGV QPEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 228 anti-FLT3/anti- FLL83 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN protein AENTVYLEMNSLKPEDTAVYICAGQVSRAYDSNWYSR DDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 229 anti-FLT3/anti- FLL94 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPEKEREFVAAISWDGGRTHYADSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAIYYCAGQVARAYDTRWYSR GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 230 anti-FLT3/anti- FLL99 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWDGGRTHYADFVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAVYYCAAQVARAYDSRWYSG GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 231 anti-FLT3/anti- FLL38 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAVSWSGGTTEIADSVKGRFTISRDN protein AKNTVYLQMSSLKPGDTAVYYCAGQVARAYDSRWYSR GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 232 anti-FLT3/anti- FLL53 QVQLQESGGGLVQAGDSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAVSQSGGTTHYADSVKGRFTISRDN protein AKNTETLVYLQMNSLKPEDTAVYYCAGQVARAYDSSW YARGDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGL VQPGNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWV SSISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNS LRPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGG GSEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAIN WVRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTI SRDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYI SYWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQ EPSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPG QAPRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGV QPEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 233 anti-FLT3/anti- FLL553 QVQLQESGGGLVQAGGSLRLSCAVSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGTTHYADSVKGRFTISRDN protein AKNTVNLVYLQMNSLRPEDTAVYYCAGQVARAYDSNW YSRGDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGL VQPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWV SSISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNS LRPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGG GSEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAIN WVRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTI SRDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYI SYWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQ EPSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPG QAPRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGV QPEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 234 anti-FLT3/anti- FLL74 QVQLQESGGGLVQAGGSLRLSCRFSGRTFSGFGTGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWAGGRTHYEDSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAVYYCAVQVSRAYDGIWYSG GDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 235 anti-FLT3/anti- FLL102 QVQLQESGGGLVQAGGSLMVSCAASGGTWSSYATGWF HSA/anti-CD3 fusion RQVPGKERKLIAGISRSGGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTSSVVYTSG NDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 236 anti-FLT3/anti- FLL122 QVQLQESGGGLVQAGGSLMVSCAASGGTWSSYATGWF HSA/anti-CD3 fusion RQVPGKERELIAGISRSGGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTSSVVYTSG NDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 237 anti-FLT3/anti- FLL134 QVQLQESGGGLVQPGGSLRLSCAASGGTFSSYATGWF HSA/anti-CD3 fusion RQVPGKEREFIAGISRNSGRTYAESVKGRFTISRDNA protein KNTVYLQMNTLRPDDTAVYYCAAARYFTRDAIYTSGD DYDYWGQGTQVTASSGGGGSGGGSEVQLVESGGGLVQ PGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVSS ISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLR PEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGS EVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWV RQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISR DDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISY WAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEP SLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQA PRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQP EDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 238 anti-FLT3/anti- FLL153 QVQLQESGGGLVQVGGSLMVSCAASGGTESSYATGWF HSA/anti-CD3 fusion RQVPGKEREFIAGVSRNSGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTGVYYCAAARYFTRDAVYTSG DDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 239 anti-FLT3/anti- FLL41 QVQLQESGGGLVQLGDSLMVSCAASGGTESSYATGWF HSA/anti-CD3 fusion RQVPGREREFIAGISRSGGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTTSVVYTSG DDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 240 anti-FLT3/anti- FLL67 QVQLQESGGGLVQLGDSLMVSCAASGGTESSYATGWF HSA/anti-CD3 fusion RQVPGKEREFIAGISRSGGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTTSVVYTSG DDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 241 anti-FLT3/anti- FLL92 QVQLQESGGGLVQAGGSLMVSCAASGGTWSSYATGWF HSA/anti-CD3 fusion RQVPGKERELIAGISRSGGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKSDDTAVYYCAAARYFTSSVVYTSG NDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 243 anti-FLT3/anti- FLL71 QVQLQESGGGLVQVGGSLMVSCAASGGTESSYATGWF HSA/anti-CD3 fusion RQVPGKEREFIAGISRNSGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTRDAVYTSG DDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 244 anti-FLT3/anti- FLL8 QVQLQESGGGLVQVGGSLMVSCAASGGTESSYATGWF HSA/anti-CD3 fusion RQVPGKEREFIAGISRNSGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTRDVVYTSG DDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 245 anti-FLT3/anti- FLL84 QVQLQESGGGLVQAGGSLMVSCAASGGTESSYATGWF HSA/anti-CD3 fusion RQVPGKEREFIAGISRSGGRTYYAESVKGRFTISRDN protein AKNTVYLQMNTLKPDDTAVYYCAAARYFTTSVVYTSG DDYDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTESKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 246 anti-FLT3/anti- FLL107 QVQLQESGGGLVQAGGSLRLSCAASGRTFSSYAMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGSNTYYADSVKGRFTISRDN protein AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 247 anti-FLT3/anti- FLL141 QVQLQESGGGLVQAGGSLRLSCAASGRTFSSYAMGWF HSA/anti-CD3 fusion RQAPGMEREFVAAISWSGYSTYYADSVKGRFTISRDD protein AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 248 anti-FLT3/anti- FLL34 QVQLQESGGGLVQAGGSLRLSCAASGRTFSSYALGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGNTYYADSVKGRFTISRDD protein AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 249 anti-FLT3/anti- FLL4 QVQLQESGGGLVQAGGSLRLSCAASERTFSSYTMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAMSWSGGSTYYADSVKGRFTISRDN protein AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 250 anti-FLT3/anti- FLL61 QVQLQESGGGLVQAGGSLRLSCAASERTFSSYAMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGSTYYADSVKGRFTISRDN protein AKNTVYLQMDSLKPEDTAVYYCAAGGSTRVVVTTTPI VKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 251 anti-FLT3/anti- FLL78 QVQLQESGGGWVQAGGSLRLSCAASGRTFSSYAMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGSSTYYADSVKGRFTISRDN protein AKNTVYLLMDSLKPEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 252 anti-FLT3/anti- FLL1 QVQLQESGGGLVQAGGSLRLSCAASGRTFSTLTVAWF HSA/anti-CD3 fusion RQAPGKEREFVVASIPSGSNTGYAESVKGRFTISRDI protein AKNTVYLQMNSLKPEDTAMYFCAARIYFGSSRGYDYW GQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNSL RLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGSG RDTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDTA VYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQLV ESGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAPG KGLEWVARIRSKYNNYATYYADQVKDRFTISRDDSKN TAYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYWG QGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTVS PGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGLI GGTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEAE YYCTLWYSNRWVFGGGTKLTVLHHHHHH 253 anti-FLT3/anti- FLL26 QVQLQESGGGLVQAGGSLRLSCAASGRTFTTYTVAWF HSA/anti-CD3 fusion RQAPGKEREFLVASIPTGSNTAYAESVKGRFTISRGN protein AKNTVYLQMNSLKPEDTAMYYCAARTYFGSSRGYDYW GQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNSL RLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGSG RDTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDTA VYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQLV ESGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAPG KGLEWVARIRSKYNNYATYYADQVKDRFTISRDDSKN TAYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYWG QGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTVS PGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGLI GGTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEAE YYCTLWYSNRWVFGGGTKLTVLHHHHHH 254 anti-FLT3/anti- FLL160 QVQLQESGGGLVQAGDSLRLSCATSGRTFNLYRVGWF HSA/anti-CD3 fusion RQAPGKEREFVARITWSADITQYADSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAIYYCATTLRKSSGIYHVDD YDDWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 255 anti-FLT3/anti- FLL173 QVQLQESGGGLVQAGGSLRLSCATSGRTFNLYRVGWF HSA/anti-CD3 fusion RQAPGKEREFVARITWSADITQYTDSVKGRFTISRDN protein AKNTVYLQMNSLKPEDTAIYYCATTLRKSSGIYHTDD YDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 256 anti-FLT3/anti- FLL178 QVQLQESGGGLVQPGGSLRLSCAASGFTFSDYAMSWV HSA/anti-CD3 fusion RQAPGKGLEWVSGISSGGYKIGYTDSTKGRFTISRDN protein AKNTLYLQMNSLTAEDTAVYYCAKGTQWSWSLRDNTS RGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNS LRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGS GRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDT AVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQL VESGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAP GKGLEWVARIRSKYNNYATYYADQVKDRFTISRDDSK NTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYW GQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTV SPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGL IGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEA EYYCTLWYSNRWVFGGGTKLTVLHHHHHH 257 anti-FLT3/anti- FLL27 QVQLQESGGGLVQPGGSLRLSCKASGFTFSSYAMSWV HSA/anti-CD3 fusion RQAPGKGLEWVSGISSGGYKIGYTDSTKGRFTISRDN protein AKNTLYLQMNSLNAEDTAVYYCAKGTQWSWALRDSTS RGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNS LRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGS GRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDT AVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQL VESGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAP GKGLEWVARIRSKYNNYATYYADQVKDRFTISRDDSK NTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYW GQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTV SPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGL IGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEA EYYCTLWYSNRWVFGGGTKLTVLHHHHHH 258 anti-FLT3/anti- FLL190 QVQLQESGGGLVQAGGSLTLSCTASGSTFSINHFSWY HSA/anti-CD3 fusion RQAPGKQRELVAFISSDGVSIDVESVKGRFTISGDND protein KNTAYLQMNGLKPEDTAVYYCYYRGFWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 259 anti-FLT3/anti- FLL43 QVQLQESGGGLVQPGGSLTLSCTASGSTFSINHFAWY HSA/anti-CD3 fusion RQAPGKQRELVAFISSDGRSTDVESVKGRFTISGDND protein KNTAYLQMNGLKPEDTAVYYCYYRGSWGQGTQVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 260 anti-FLT3/anti- FLL15 QVQLQESGGGLVQAGGSLSLSCAASEGTISHAAMGWF HSA/anti-CD3 fusion RQAPGKERQFVAYDTWTGGSTNYADSVKDRFTITGDH protein AKNTVYLQMNSLKPEDTGVYYCAVRGRYSASYTYTNP ASYKYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLV QPGNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVS SISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSL RPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGG SEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINW VRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTIS RDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYIS YWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQE PSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQ APRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQ PEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 261 anti-FLT3/anti- FLL45 QVQLQESGGGLVQAGGSLRLSCAASGGTFSSSAMGWF HSA/anti-CD3 fusion RQAPGKEREFVATITQNDVPTYYTHSVKGRFTISRDN protein AKNTMYLQMNSLKPEDTAVYYCAQRVAQASGWRTTIK DYGYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQ PGNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSS ISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLR PEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGS EVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWV RQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISR DDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISY WAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEP SLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQA PRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQP EDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 262 anti-FLT3/anti- FLL39 QVQLQESGGGLVQAGGSLRLSCAASGLTSSTYRMAWF HSA/anti-CD3 fusion RQAPGKEREFAAGISYSADSGGSTNYADSVKGRFTIS protein RDNAKNTVYLQMSSLKPEDTAVYYCAAGRYSGTYNSP YSSSYVYWGQGTQVTVSSGGGGSGGGSEVQLVESGGG LVQPGNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEW VSSISGSGRDTLYADSVKGRFTISRDNAKTTLYLQMN SLRPEDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSG GGSEVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAI NWVRQAPGKGLEWVARIRSKYNNYATYYADQVKDRFT ISRDDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSY ISYWAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVT QEPSLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKP GQAPRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSG VQPEDEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 263 anti-FLT3/anti- FLL177 QVQLQESGGGLVQTGGSLRLSCAASGSTFSRNTMGWF HSA/anti-CD3 fusion RQAPGKERVFVLGISWSGIRSYYLDSAKARFTISRDN protein AKNTVYLQMNSLRPEDTAVYYCAAQEGSSPGPYKYWG QGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNSLR LSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGSGR DTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDTAV YYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQLVE SGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAPGK GLEWVARIRSKYNNYATYYADQVKDRFTISRDDSKNT AYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYWGQ GTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTVSP GGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGLIG GTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEAEY YCTLWYSNRWVFGGGTKLTVLHHHHHH 264 anti-FLT3/anti- FLL823 QVQLQESGGGVVQVGGSLRLSCAASGGTFGYYAVGWF HSA/anti-CD3 fusion RQAPGKEREFVAAVTWNGAYLYSDPVKGRFTISRDNA protein KNTVYLQMNSLKSEDTAVYYCGLDRWSAVVESTPSTR GQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNSL RLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGSG RDTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDTA VYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQLV ESGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAPG KGLEWVARIRSKYNNYATYYADQVKDRFTISRDDSKN TAYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYWG QGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTVS PGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGLI GGTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEAE YYCTLWYSNRWVFGGGTKLTVLHHHHHH 265 anti-FLT3/anti- FLL76 QVQLQESGGGLVQAGGSLRLSCAASGGAFSSYVMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAVISWSGRITDYADSVKGRFSISRD protein NAKSTVYLQMNNLKPEDTAVYYCAAKTGMYIDLRTST FDYWGQGTQVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 266 anti-FLT3/anti- FLL822 QVQLQESGGGSVQAGGSLRLSCTASGRTFTDYTMGWF HSA/anti-CD3 fusion RQAPGKEREFMLGISSNGYRRYYTGSMKDRFTISRDN protein VKKTVYLQMNDLKPEDTAVYYCAASEDHGAPRYDYWG QGTQVTVSSGGGGSGGGSEVQLVESGGGLVQPGNSLR LSCAASGFTFSKFGMSWVRQAPGKGLEWVSSISGSGR DTLYADSVKGRFTISRDNAKTTLYLQMNSLRPEDTAV YYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQLVE SGGGLVQPGGSLKLSCAASGFTFNKYAINWVRQAPGK GLEWVARIRSKYNNYATYYADQVKDRFTISRDDSKNT AYLQMNNLKTEDTAVYYCVRHANFGNSYISYWAYWGQ GTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPSLTVSP GGTVTLTCASSTGAVTSGNYPNWVQQKPGQAPRGLIG GTKFLVPGTPARFSGSLLGGKAALTLSGVQPEDEAEY YCTLWYSNRWVFGGGTKLTVLHHHHHH 267 anti-FLT3/anti- FLH107 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYAMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGSNTYYADSVKGRFTISRDN protein SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 268 anti-FLT3/anti- FLH141 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYAMGWF HSA/anti-CD3 fusion RQAPGMEREFVAAISWSGYSTYYADSVKGRFTISRDN protein SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 269 anti-FLT3/anti- FLH19C EVQLVESGGGLVQPGGSLTLSCAASGSTFSINHFSWY HSA/anti-CD3 fusion RQAPGKQRELVAFISSDGVSIDVESVKGRFTISGDNS protein KNTAYLQMNSLRAEDTAVYYCYYRGFWGQGTLVTVSS GGGGSGGGSEVQLVESGGGLVQPGNSLRLSCAASGFT FSKFGMSWVRQAPGKGLEWVSSISGSGRDTLYADSVK GRFTISRDNAKTTLYLQMNSLRPEDTAVYYCTIGGSL SVSSQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQPG GSLKLSCAASGFTFNKYAINWVRQAPGKGLEWVARIR SKYNNYATYYADQVKDRFTISRDDSKNTAYLQMNNLK TEDTAVYYCVRHANFGNSYISYWAYWGQGTLVTVSSG GGGSGGGGSGGGGSQTVVTQEPSLTVSPGGTVTLTCA SSTGAVTSGNYPNWVQQKPGQAPRGLIGGTKFLVPGT RARFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYSNR WVFGGGTKLTVLHHHHHH 270 anti-FLT3/anti- FLH34 EVQLLESGGGLVQPGGSLTLSCAASGRTFSSYALGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGGNTYYADSVKGRFTISRDN protein SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 271 anti-FLT3/anti- FLH4 EVQLLESGGGLVQPGGSLTLSCAASERTFSSYTMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAMSWSGGSTYYADSVKGRFTISRDN protein SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 272 anti-FLT3/anti- FLH78 EVQLLESGGGLVQPGGSLTLSCAASGRTESSYAMGWF HSA/anti-CD3 fusion RQAPGKEREFVAAISWSGSSTYYADSVKGRFTISRDN protein SKNTLYLQMNSLRAEDTAVYYCAAGGSTRVVVTTTPV VKYWGQGTLVTVSSGGGGSGGGSEVQLVESGGGLVQP GNSLRLSCAASGFTFSKFGMSWVRQAPGKGLEWVSSI SGSGRDTLYADSVKGRFTISRDNAKTTLYLQMNSLRP EDTAVYYCTIGGSLSVSSQGTLVTVSSGGGGSGGGSE VQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWVR QAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISRD DSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISYW AYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEPS LTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQAP RGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQPE DEAEYYCTLWYSNRWVFGGGTKLTVLHHHHHH 372 sdAb Anti- EVQLVESGGGLVQPGNSLRLSCAASGFTESKFGMSWV albumin RQAPGKGLEWVSSISGSGRDTLYADSVKGRFTISRDN AKTTLYLQMNSLRPEDTAVYYCTIGGSLSVSSQGTLV TVSS 373 scFv Anti- EVQLVESGGGLVQPGGSLKLSCAASGFTFNKYAINWV CD3 RQAPGKGLEWVARIRSKYNNYATYYADQVKDRFTISR DDSKNTAYLQMNNLKTEDTAVYYCVRHANFGNSYISY WAYWGQGTLVTVSSGGGGSGGGGSGGGGSQTVVTQEP SLTVSPGGTVTLTCASSTGAVTSGNYPNWVQQKPGQA PRGLIGGTKFLVPGTPARFSGSLLGGKAALTLSGVQP EDEAEYYCTLWYSNRWVFGGGTKLTVL 374 Tag 6x-His HHHHHH 375 linker G4SG3S GGGGSGGGS 376 Sortase LPETG 377 linker (GS)_(n) (GS)_(n) 378 linker (GGS)_(n) (GGS)_(n) 379 linker (GGGS)_(n) (GGGS)_(n) 380 linker (GGSG)_(n) (GGSG)_(n) 381 linker (GGSGG)_(n) (GGSGG)_(n) 382 linker (GGGGS)_(n) (GGGGS)_(n) 383 linker (GGGGG)_(n) (GGGGG)_(n) 384 linker (GGG)_(n) (GGG)_(n) 385 linker GGGGSGGGGSGGGGSGGGGS 386 linker GGGGSGGGGSGGGGS 387 linker GGGGSGGGS 388 P36888 MPALARDGGQLPLLVVFSAMIFGTITNQDLPVIKCVL INHKNNDSSVGKSSSYPMVSESPEDLGCALRPQSSGT VYEAAAVEVDVSASITLQVLVDAPGNISCLWVFKHSS LNCQPHFDLQNRGVVSMVILKMTETQAGEYLLFIQSE ATNYTILFTVSIRNTLLYTLRRPYFRKMENQDALVCI SESVPEPIVEWVLCDSQGESCKEESPAVVKKEEKVLH ELFGTDIRCCARNELGRECTRLFTIDLNQTPQTTLPQ LFLKVGEPLWIRCKAVHVNHGFGLTWELENKALEEGN YFEMSTYSTNRTMIRILFAFVSSVARNDTGYYTCSSS KHPSQSALVTIVEKGFINATNSSEDYEIDQYEEFCFS VRFKAYPQIRCTWTFSRKSFPCEQKGLDNGYSISKFC NHKHQPGEYIFHAENDDAQFTKMFTLNIRRKPQVLAE ASASQASCFSDGYPLPSWTWKKCSDKSPNCTEEITE GVWNRKANRKVEGQWVSSSTLNMSEAIKGFLVKCCAY NSLGTSCETILLNSPGPFPFIQDNISFYATIGVCLLF IVVLTLLICHKYKKQFRYESQLQMVQVTGSSDNEYFY VDFREYEYDLKWEFPRENLEFGKVLGSGAFGKVMNAT AYGISKTGVSIQVAVKMLKEKADSSEREALMSELKMM TQLGSHENIVNLLGACTLSGPIYLIFEYCCYGDLLNY LRSKREKFHRTWTEIFKEHNFSFYPTFQSHPNSSMPG SREVQIHPDSDQISGLHGNSFHSEDEIEYENQKRLEE EEDLNVLTFEDLLCFAYQVAKGMEFLEFKSCVHRDLA ARNVLVTHGKVVKICDFGLARDIMSDSNYVVRGNARL PVKWMAPESLFEGIYTIKSDVWSYGILLWEIFSLGVN PYPGIPVDANFYKLIQNGFKMDQPFYATEEIYIIMQS CWAFDSRKRPSFPNLTSFLGCQLADAEEAMYQNVDG RVSECPHTYQNRRPFSREMDLGLLSPQAQVEDS 389 FLT3 antibody FLH92a EVQLLESGGGLVQPGGSLTLSCAASGGTWSSYA variable domain TGWFRQAPGKERELIAGISRSGGRTYYADSVKG RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAAA RYFTSSVVYTSGNDYDYWGQGTLVTVSS 390 FLT3 antibody FLH92b EVQLLESGGGLVQPGGSLTLSCAASGGTWSSYA variable domain TGWFRQAPGKERELIAGISRSGGRTYYADSVKG RFTISRDNSKNIVYLQMNSLRAEDTAVYYCAKA RYFTSSVVYTSGNDYDYWGQGTLVTVSS 391 anti-FLT3/anti- FLH92a EVQLLESGGGLVQPGGSLTLSCAASGGTWSSYA HSA/anti-CD3 fusion TGWFRQAPGKERELIAGISRSGGRTYYADSVKG protein RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAAA RYFTSSVVYTSGNDYDYWGQGTLVTVSSGGGGS GGGSEVQLVESGGGLVQPGNSLRLSCAASGFTF SKFGMSWVRQAPGKGLEWVSSISGSGRDTLYAD SVKGRFTISRDNAKTTLYLQMNSLRPEDTAVYY CTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQL VESGGGLVQPGGSLKLSCAASGFTFNKYAINWV RQAPGKGLEWVARIRSKYNNYATYYADQVKDRF TISRDDSKNTAYLQMNNLKTEDTAVYYCVRHAN FGNSYISYWAYWGQGTLVTVSSGGGGSGGGGSG GGGSQTVVTQEPSLTVSPGGTVTLTCASSTGAV TSGNYPNWVQQKPGQAPRGLIGGTKFLVPGTPA RFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYS NRWVFGGGTKLTVLHHHHHH 392 anti-FLT3/anti- FLH92b EVQLLESGGGLVQPGGSLTLSCAASGGTWSSYA HSA/anti-CD3 fusion TGWFRQAPGKERELIAGISRSGGRTYYADSVKG protein RFTISRDNSKNIVYLQMNSLRAEDTAVYYCAKA RYFTSSVVYTSGNDYDYWGQGTLVTVSSGGGGS GGGSEVQLVESGGGLVQPGNSLRLSCAASGFTF SKFGMSWVRQAPGKGLEWVSSISGSGRDTLYAD SVKGRFTISRDNAKTTLYLQMNSLRPEDTAVYY CTIGGSLSVSSQGTLVTVSSGGGGSGGGSEVQL VESGGGLVQPGGSLKLSCAASGFTFNKYAINWV RQAPGKGLEWVARIRSKYNNYATYYADQVKDRF TISRDDSKNTAYLQMNNLKTEDTAVYYCVRHAN FGNSYISYWAYWGQGTLVTVSSGGGGSGGGGSG GGGSQTVVTQEPSLTVSPGGTVTLTCASSTGAV TSGNYPNWVQQKPGQAPRGLIGGTKFLVPGTPA RFSGSLLGGKAALTLSGVQPEDEAEYYCTLWYS NRWVFGGGTKLTVLHHHHHH 89 CDR1 FLH92a GGTWSSYATG 89 CDR1 FLH92b GGTWSSYATG 393 CDR2 FLH92a GISRSGGRTYYADSVKG 394 CDR2 FLH92b GISRSGGRTYYADSVKG 173 CDR3 FLH92a ARYFTSSVVYTSGNDYDY 173 CDR3 FLH92b ARYFTSSVVYTSGNDYDY 300 framework 1 FLH92a EVQLLESGGGLVQPGGSLTLSCAAS 300 framework 1 FLH92b EVQLLESGGGLVQPGGSLTLSCAAS 395 framework 2 FLH92a WFRQAPGKERELIA 395 framework 2 FLH92b WFRQAPGKERELIA 364 framework 3 FLH92a RFTISRDNSKNTLYLQMNSLRAEDTAVYYCAA 396 framework 3 FLH92b RFTISRDNSKNTVYLQMNSLRAEDTAVYYCAK 371 framework 4 FLH92a WGQGTLVTVSS 371 framework 4 FLH92b WGQGTLVTVSS 397 CD3 binder GFTFNKYAIN exemplary HC CDR1 (heavy chain CDR1) 398 CD3 binder RIRSKYNNYATYYADQVK exemplary HC CDR2 399 CD3 binder HANFGNSYISYWAY exemplary HC CDR3 400 CD3 binder ASSTGAVTSGNYPN exemplary LC CDR1 (light chain CDR1) 401 CD3 binder GTKFLVP exemplary LC CDR2 402 CD3 binder TLWYSNRWV exemplary LC CDR3 403 HSA binder GFTFSKFGMS exemplary CDR1 404 HSA binder SISGSGRDTLYADSVK exemplary CDR2 405 HSA binder GGSLSV exemplary CDR3 

1.-30. (canceled)
 31. An FLT3 binding domain comprising at least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein a) the CDR1 comprises the amino acid sequence of SEQ ID NO: 100, the CDR2 comprises the amino acid sequence of SEQ ID NO: 151, and the CDR3 comprises the amino acid sequence of SEQ ID NO: 186; b) the CDR1 comprises the amino acid sequence of SEQ ID NO: 89, the CDR2 comprises the amino acid sequence of SEQ ID NO: 393, and the CDR3 comprises the amino acid sequence of SEQ ID NO: 173; or c) the CDR1 comprises the amino acid sequence of SEQ ID NO: 89, the CDR2 comprises the amino acid sequence of SEQ ID NO: 394, and the CDR3 comprises the amino acid sequence of SEQ ID NO:
 195. 32. The FLT3 binding domain of claim 31, comprising an amino acid sequence that is at least 80% identical to a sequence selected from the group consisting of SEQ ID Nos. 73, 389, or
 390. 33. The FLT3 binding domain of claim 31, comprising an amino acid sequence selected from the group consisting of SEQ ID Nos. 73, 389, or
 390. 34. The FLT3 binding domain of claim 33, wherein the FLT3 binding domain is a single domain antibody (sdAb).
 35. The FLT3 binding domain of claim 31, wherein the FLT3 binding domain is part of a bispecific antibody.
 36. The FLT3 binding domain of claim 34, wherein the bispecific antibody comprises a CD3 binding domain.
 37. The FLT3 binding domain of claim 36, wherein the CD3 binding domain is a single chain variable fragment (scFv).
 38. The FLT3 binding domain of claim 37, wherein the CD3 is a human CD3.
 39. The FLT3 binding domain of claim 31, wherein the FLT3 binding domain is part of a multispecific antibody.
 40. A multispecific antibody comprising the FLT3 binding domain of claim 31, a CD3 binding domain and an albumin binding domain.
 41. The multispecific antibody of claim 39, wherein the CD3 binding domain is an scFv.
 42. The multispecific antibody of claim 40, wherein the CD3 binding domain comprises the amino acid sequence of SEQ ID No.
 373. 43. The multispecific antibody of claim 40, wherein the CD3 is a human CD3.
 44. The multispecific antibody of claim 40, wherein the albumin binding domain is a single domain antibody (sdAb).
 45. The multispecific antibody of claim 40, wherein the albumin binding domain comprises the amino acid sequence of SEQ ID No.
 372. 46. The multispecific antibody of claim 40, wherein the albumin is a human serum albumin.
 47. The multispecific antibody of claim 40, wherein the multispecific antibody is a single chain polypeptide and the FLT3 binding domain, the CD3 binding domain, and the albumin binding domain are joined in any order from N-terminus to C-terminus.
 48. The multispecific antibody of claim 40, wherein multispecific antibody comprises an amino acid sequence selected from the group consisting of SEQ ID Nos. 269, 391, and
 392. 49. The FLT3 binding domain of claim 31, wherein the FLT3 binding domain binds to human FLT3.
 50. An FLT3 targeting trispecific protein comprising (A) a first domain that binds a human CD3; (B) a second domain that binds a human serum albumin protein; and (C) a third domain that binds a human FLT3, wherein the third domain that binds the human FLT3 comprises at least three complementarity determining regions (a CDR1, a CDR2, and a CDR3), wherein a) the CDR1 comprises the amino acid sequence of SEQ ID NO: 100, the CDR2 comprises the amino acid sequence of SEQ ID NO: 151, and the CDR3 comprises the amino acid sequence of SEQ ID NO: 186; b) the CDR1 comprises the amino acid sequence of SEQ ID NO: 89, the CDR2 comprises the amino acid sequence of SEQ ID NO: 393, and the CDR3 comprises the amino acid sequence of SEQ ID NO: 173; or c) the CDR1 comprises the amino acid sequence of SEQ ID NO: 89, the CDR2 comprises the amino acid sequence of SEQ ID NO: 394, and the CDR3 comprises the amino acid sequence of SEQ ID NO:
 195. 51. The FLT3 targeting trispecific protein of claim 50, wherein the first domain is an scFv that comprises a heavy chain comprising HC CDR1, HC CDR2, HC CDR3, and a light chain comprising LC CDR1, LC CDR2, or LC CDR3, wherein the HC CDR1 comprises the amino acid sequence of SEQ ID NO: 397; the HC CDR2 comprises the amino acid sequence of SEQ ID NO: 398; the HC CDR3 comprises the amino acid sequence of SEQ ID NO: 399; the LC CDR1 comprises the amino acid sequence of SEQ ID NO: 400; the LC CDR2 comprises the amino acid sequence of SEQ ID NO: 401; and the LC CDR3 comprises the amino acid sequence of SEQ ID NO:
 402. 52. The FLT3 targeting trispecific protein of claim 51, wherein the first domain comprises an amino acid sequence that is at least 90% identical to the sequence set forth in SEQ ID No.
 373. 53. The FLT3 targeting trispecific protein of claim 50, wherein the second domain is an sdAb that comprises a CDR1, a CDR2, and a CDR3, wherein the CDR1 comprises the amino acid sequence of SEQ ID NO: 403 the CDR2 comprises the amino acid sequence of SEQ ID NO: 404; and the CDR3 comprises the amino acid sequence of SEQ ID NO:
 405. 54. The FLT3 targeting trispecific protein of claim 53, wherein the second domain comprises an amino acid sequence that is at least 90% identical to the sequence set forth in SEQ ID No.
 372. 55. A method of treating a hematologic malignancy in a subject, the method comprising administering to the subject a FLT3 targeting trispecific protein according to claim
 50. 56. The method of claim 55, wherein the third domain that binds to a human FLT3 comprises an amino acid sequence that is at least 80% identical to a sequence selected from the group consisting of SEQ ID NO: 73, 389, or
 390. 57. The method of claim 56, wherein the trispecific protein comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 269, 391, and
 392. 58. The method of claim 57, wherein the hematologic malignancy is an acute myeloid leukemia (AML), a myelodysplastic syndrome, or a chronic myelomonocytic leukemia. 